Greetings all, first post here.
Please note that it's not reliable to test a third-party PS1 memory card on a PS2 system since the PS2 expects the card to have the encrypted Sony key on it, and if it doesn't the memory card will not appear at all in the system browser. Some third party cards may then seem not to work when you try it on a PS2 but if you plug it in a PS1 the files may be there, just that the memory card is not recognized.
My personal blog is written in french but
this post illustrates the problem, with a bit of Google translate + pictures it should be fairly self-explanatory.
My advise would be to try the card on a PS1 system and see if your files are there. And yes, by all means, use official cards whenever possible.