[ATM] Fine Grind already Blanchard ground mirror blank back?

["Michael Fremont" <fremontmj@gmail.com>]

I just received a 16" 1.625" thick pyrex blank from Newport Glass.  It
is pregenerated to f4.5 and Blanchard ground on the back.

Having looked through the archive, I'm still unsure whether I should
fine grind the back at 220 grit even though it's Blanchard ground; and
am further unsure that I can even do it, since the front already has a
curve.

Thanks in advance for helping this newbie.

Mike
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