I just saw the expression 'Maraming masasayang kwento...' and it

@JohnD
It is quite common and required in formal speech. I do see it a lot, maybe you just hadn't been looking for it?

@JohnD Yes. According to a book I just acquired (but its 30 years old) ma- adjectives can be pluralized like this. However it only applies to ma-.

Here you go:

@AMBoy Thank you. That partially explains my lack of observance - but since so many Tagalog adjectives do start with ma- , my lack of attention is probably still mostly to blame!
I wonder also if it is used in expressions like 'My legs hurt'. Is the correct Tagalog Masasakit ang mga binti ko?
I still have a sneaking suspicion there are other exceptions. But maybe it is just my total lack of observation.

@JohnD I'll leave that one for the experts but seems plausible though they don't really tend to pluralize lets and feet too often from what I can remember (but this might just be lack of exposure on my part).

@jkos I think my lack of attention is probably the main factor! But from the response below, it does seem to be kind of optional. There are no doubt guidelines as to when it is appropriate though and when not.

@AMBoy Actually that is quite an interesting thought in its own right. I am a novice but I have a feeling that Tagalog plurals may be a little bit different from English plurals. In English we have singular and plural. Am I right in thinking that Tagalog has one, two and plural? There is just a thought at the back of my brain about this and I may be completely wrong.

I read somewhere else, its really up to you, mga or marororoot. @akosikoneho actually did a review of the corpus and found magagandan used slightly more (basically a tie) than mga magandang, if I remember correctly. I was surprised because in my mind "mga" is the best.

@JohnD I'm a novice as well, I don't know the answer but I've been told that plurals in Tagalog are not quite the same. I'll wait for feedback from the experts.

@AMBoy So it is another way of showing a plural? I hadn't thought of that. I was thinking that if the noun was plural and had an adjective, you would use both mga and replicate the adjective eg ang mga mabubuting tao. I think you are suggesting that you use one or the other eg 'ang mga mabuting tao' or 'ang mabubuting tao'. That would certainly explain why it is not seen all the time.

@JohnD Yes, in your example its either/or, but I have seen some using both at the same time, I don't think that's required, or even proper but maybe its "acceptable"?, but again, I don't want to be the blind leading the blind here. I hate when others do that. So please take it with a grain of salt and lets see what the natives say.

@AMBoy Blind leading the blind. I had a hilarious experience about 20 years ago when I was doing some Tagalog lessons in the Philippines. After the lesson, I got onto a jeepney with a Japanese co-student. We couldn't speak a word of each other's languages so had to try to communicate in Tagalog. We could just see the other passengers trying to work out what the hell was going on.

Using MGA is more important that reduplication in ma- adjectives.magandang mga babae and mga magagandang mga babae are acceptable."Papagod" na tao is very awkward. It sounds like "going to be tired".Stick to MGA + adjectiveI'm less versed technically than Koneho, but the reduplication so we'll have to wait for him for the technical aspect.Papagod is awkward, as well as guguwapong/popoging mga lalaki. (The latter sounds like "going to be handsome men")However, ANG guguwapo ng mga lalaki and ANG popogi ng mga lalaki are accepted and common expressions.As a learner, it's safer to stick to MGA + adjective + noun without the reduplication.

@JohnDI recently read about pluralization in Tagalog Reference Grammar. Basically duplication is only for ma- adjectives. There are also many ways to pluralize ma- adjectives. Here's page 231. You should start reading from page 229 though as there are some exceptions. You can get the book from the Resources tab.

@Bituingmaykinang Thank you. Yes, for my level it is definitely a matter of keep it simple. Providing it is right of course. Mga singular adjective noun (eg mga matalinong bata) is of course understandable and it also seems to be correct. Probably best to stick with that til I reach a higher level.
Still it is good to know the other structures so that when I see them in Tagalog I know what is going on.