Yellow motherboards - I see no yellow motherboards? My (green) motherboard has all the C= marks and also original Commodore ROMS and sits in the Original CBM case. Mine is pretty much identical to the motherboard in the article you link to.
It's green with yellow traces but I call that yellow. It's like a lot of the C= proto boards. Most C= motherboards are all green with green traces like yours.
Check your ROMS - the rev4 version from AT - has a ROM that says Amiga 1995: http://www.bigbookofamigahardware.com/bboah/media/download_photos/a4000tmb_rev4_4.jpg
They have hand written labels "4.70 Byte 0" and "4.70 Byte 1" and look to be Eproms.
You can also Check Ramsey on the AT version it also says Amiga 1995.
No Amiga on mine. It has a "C= CSG" at the top and says "CBM 1989". It is a revision 7.
If you have Commodore ROMS 1994 - it's probably a CBM motherboard.
It's defiantly unusual and probably is an early C= version.
WTH is up with the battery on that MB? LOL.
It's just the stock soldered on lithium coin cell flipped upward. The 4000T came that way so leaking NiCad batteries are not a problem.