I notice that these processors are sometimes spelled with "C" and sometimes not, like 65C02. Why is that; does the "C" mean Commodore? Is it more official when spelled with a "C?"

CMOS, generally. The 65C02 specifically is a partial redesign that adds some new instructions and tidies up a few issues compared to the original NMOS 6502.

Yes.

True, but as you probably know, that's incidental.

As compared to the older NMOS process, CMOS is a chip fabrication technology noted for attributes including better noise immunity and much lower power consumption.

It would've been possible and beneficial to simply migrate the old 6502 directly to CMOS. But it happens to be a good opportunity for making improvements, given that a redesign will be required in any case.

-- Jeff

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?