I didn't say anything about being able to play/use them, just about knowing what they do.
But wouldn't you agree that the fact that Matoran can't use them is probably a factor in why they don't memorize them all?
As it's their job to produce masks, I think knowing which masks provide which powers is relevant to their line of work, regardless of whether they can use the masks themselves.
I thought this was answered earlier -- Vakama had only just started making Great Masks (and I presume Nobles), so his specialty was in Matoran masks (Nuhrii's appears to be as well incidentally). Which requires knowing the shapes, but not powers.
There's various cautions to this but I think it's been covered well enough in other posts and the seemingly five thousand other topics like this we seem to get every month or so lol. Also I agree with fishers that he may know the right disk mixtures but not associate that with the powers.
It's also possible someone else does the actual mixing. The scene were Vakama expresses amazement at the sight of fusing two of the Great Disks may be evidence that he'd never actually done it himself.
Well, I could say that Matoran see Toa using masks for stunts and feats that are arguably entertaining to watch, so there could be some motivation to know how they work as well, even if the Matoran can't pull it off themselves.
I don't get that kind of vibe from their culture. It wasn't like they plopped down on a couch after work to watch CSI: Metru Nui. Unless you were personally a witness to an incident where a Toa was involved you would be unlikely to know much of what happened, and they were very work-focused. Likely nobody would have the time to package presentations that would make this information easily available in entertaining formats. They were all too busy doing various jobs that kept the city's physical machinery operational.
Also they hadn't had Toa for a while apparently and it may be that few or none of the Mangai had mask powers that were shared by the Metru.
What's your evidence for this? In their first discussion, Vakama says "finding (the Disks) would prove to Turaga Dume that we are worthy Toa", then Nokama says they will present them to Dume because "he will know what to do." Plus the start of comic 19 states: "The Toa Metru traveled to the Coliseum, expecting to be hailed as heroes for finding the Great Disks and defeating the Morbuzahk." At no point before the Coliseum trip do they express any doubts about him.
Pretty sure Vakama thought something along those lines in one of the books. I don't have time now to re-read them line by line again (and it might have been one I had to get from the library and just returned), but I seem to recall that. In any event, one thing they oddly never doubted was that Dume would consider it possible they were not true Toa, since they sought to use the Great Disks as proof. You would think a wise elder who had been a Toa himself would know one when he saw one.
Plus, again, the Vahki clearly had not been ordered to welcome any Toa on sight (the city would logically be in dire need of them since the Mangai disappeared other than Lhikan) -- the Vahki were giving the Metru trouble from day one and this never seems to strike them as unexpected. So it's clear they realized something was wrong with him. Likely they just attributed it to paranoia after hundreds of years of repeated attempts by the Dark Hunters to take over the city which had recently resulted in the announcement they would have all heard about closing the sea gates. Dume controls the Vahki, so their behavior speaks clearly to Dume's state of mind.
Although I don't know if I would phrase it as "doubting" him. If you notice my main point was actually that they did NOT doubt him. They just seemed to think that events had affected him deeply and it made proving themselves to him difficult (but had he been the real Dume, the entrance to the Coliseum scene would have been all the proof he would need, obviously). Actually my point was that only if they had doubted him would they feel any need to delay going before him in order to learn their mask powers first. Think about it -- since they "knew" that he would obviously accept the proof, why would any of them say, "hey guys, maybe we'd better prepare for this meeting by learning our mask powers first"?
No -- because they didn't doubt him (and because they assumed, thus, that the trouble was over with now that the Morbuzakh was defeated), they assumed they would have plenty of time to learn their powers after meeting Dume.
But to address the original point, even if 'Dumakuta' managed to keep the Toa away from any learning sites, couldn't the Toa ask Matoran friendly to them to go in and find out the masks powers then relay the information back to them?
Yes, but they wouldn't have thought of this prior to the Coliseum, since it would obviously make more sense just to "kill two birds with one stone" -- since they'd had to rush to get the Great Disks in order to rush to defeat "the" threat to the city, they now had easy proof for Dume anyways of their worthiness. So why not just go to him and have him tell the Vahki to leave them alone?
And afterward they were being chased constantly (and three arrested).
One other issue is that Lhikan could have told them... I seem to recall he said something about how it was better for them to figure them out themselves, though. (And he did help some of them figure it out while in the prison.)
Edit: Also, I doubt there would have been any Matoran who would defy the Vahki for a bunch of humanoid strangers. There's a scene in Adventures #1 where a Matoran is guarding a locked entrance to where Nuhrii works, and Vakama tells this guard that Nuhrii's life may be on the line, but the Matoran refuses to let him in, citing as reason that the Vahki had forbidden it. The Vahki were the law (literally; it's what the name means ); you didn't disobey them. The Matoran apologized for it but insisted he must obey; he feared what the result would be if he disobeyed (I believe he feared he would lose his job... don't quote me on that part though).
This is even while knowing that Nuhrii's life is in danger. This Matoran would probably personally know Nuhrii, since they work at the same place and he would let Nuhrii in every day, and obviously he knew who he was at the least.
If it's like that throughout the city, there wouldn't have been anyone to do that. Maybe the Great Disk Matoran, but they were trying not to let any of those out of their sight precisely because they knew one of them must be the traitor.
And let's not miss the elephant in the room here -- the Vahki weren't stopping the "green spiderlike guy" that was attacking them, who they probably assumed was a Dark Hunter. So that would, I'd think, raise major alarm bells even if it more subconscious than conscious.
Bottom line is, I see good reasons both ways not to learn the powers before proving themselves. Whatever suspicions they had (as long as they didn't suspect Dume was a fake) would make them want to avoid the learning centers, and whatever naivete they had would make them assume they didn't need to go there before the Coliseum. Wherever they actually fell on that spectrum, the result is the same, logically. Only if they could have imagined Dume was really the Makuta would they try to 'cheat' to learn the powers.