I owned several of them at one time, and like you, lots of mags.
Which models did you have? I bought a crate of them very soon after they first came into Canada. All of them had "steel" butt plates, none of them had povisions for selector switches, and all had Chu wood stocks.
I don't know, and neither did the distributor I bought them from, whether or not they were intended for Chinese military issue or for sale to some other nation, such as the US, Africa, etc.
I sold them all, except one, which I kept until it looked like they were headed for restricted classification.
I was very early, to sell, but in truth, I wasn't using it much, because I preferred the stock, fixed mag, model.
I cleaned the cosmoline out of all of them and tested them with a mixed mags and mixed manufacturers of ammo.
I never had any issues with the magazines that came with each rifle (two).
I bought two boxes of ten each, aftermarket mags, and they were so unpredictable that I just gave them to the folks purchasing the rifles. They were informed of the unpredictability.
I never had any complaints from anyone I sold the rifles to, but I will admit I have heard complaints about the later "commercial" variants.