I found a weird SCPH-7501. It's a SCPH 7501 with a PU-18 board

Today at a Florida vacation, I bought two fat PS1's off a Facebook marketplace which had a July 1997 Scph-5501 and this weird SCPH-7501 made August 1998 with a PU-18/SCPH-5501 bottom plastic. An SCPH-7501 would normally have a PU-22 and a KSM-440AEM and more vents in the plastic bottom.
Here are some photos if you want to see.
This is the console in question:








I first heard about SCPH-7501's having PU-18's in them that TriMesh in a post saying Early Mexican SCPH-7501 has a PU-18. The one I have is not a Mexican and says was Made in Japan.
Are these either rare, parts were swapped or leftover parts from production?

This is what I first heard of: https://assemblergames.com/threads/best-playstation-1-model.51396/

 

Well, one odd thing is that the serial numbers on the controller port and the case bottom don't fit.

 

Honestly, really hard to tell - although the dogeared corner and the little crease at the bottom of the label makes me suspect someone might have just swapped the label over. I guess it's possible that one of the Japanese factories might have had left over US spec PU-18 boards, but the gap between the date codes on the PCB and the date on the housing is about a year, which is a really long time by consumer electronics manufacturing standards.