I was thinking the same as Veronica... The eproms  are probably slower=20
devices than the original master eprom and the test circuit is running=20
faster than the "burned" eproms  can be clocked.
This would cause the "problem" of them being "dead" on the test circuit=20
but still verifying as programed correctly.
You probably got a batch of slow (or mis-marked) eproms.  This may have=20
been done on purpose if they came as  "special price items".  Remarking=20
ICs to a "faster" speed makes them more profitable to the seller but=20
worthless to the buyer.
Dave
--=20
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