These chips have never been made by UMC. As much as I know the W65C02S8P-10 reference was only made by WDC.
I found another thread here:
http://forum.6502.org/viewtopic.php?f=12&t=4277
This chip seems not to be compatible with the additional 65C02 opcodes
And here:
http://www.vcfed.org/forum/showthrea...vs-65C02/page2
a user said that this chip is not working in his old apple IIe. So whatever it may be, it is not a real W65C02S8P-10-compatible chip