Japanese PS1 Game Product Number Variations?

So a few weeks ago I had some Japanese Import Playstation games traded in to my store.
They all play the exact same as the official JP release, but they have different product numbers.
For instance, IQ Final has a product number of PAPX 90063 instead of SLPS ### or whatever.
I think these games were rentals? My understanding is that rentals were illegal in Japan, unless allowed by the copyright holder. Any info on these variations would be appreciated!

 

I think games which start with PAPX are usually trials or previews, hence the 'not for sale' text. Also PCPX or SLPM product numbers.

 

Look here:
https://translate.google.com/transl...-size.net:80/slps/num.html&edit-text=&act=url

 

体験版 (taikenban) is "trail version". The red sticker on pocket muumuu says "free of charge rental version" - but that also has a taikenban marking.

 

Thank you!!

 

PlayStation Datacenter site can be very helpful in these situations.