Does that mean it doesn't recognize any other chips on that board? In
that case, we really are dealing with a missing board enable routine and
my patch just papers over the bug.
Do you have another board where the chip fits and where an unpatched
flashrom recognizes it?

Yes flashrom doesn't recognize these chips (patched and unpatched)
AT-29C020, W29C020C-90B, supported by flashrom
Uniflash recognizes sst29ee010 chip and writes it. Chip is unsupported by flashrom.
Writing with flashrom would be much more comfortable.
 
Unfortunately I don't have another board which recognizes this W29C020-12 chip.