I do remember running across some a while back that
were marked "IBM" and had
a pinout that was different enough from the usual kind that they would not
work in most equipment that they were tried in. Is that what those were?
Possiby RS/6000 SIMMS? these are 72-pin (x40? bit) SIMMS with a not-quite-so-deep cut on
the one side.
I found one non-IBM that would tolerate them (had 1/2 of a bank of 16MB ones, a bank on a
RS/6k POWER2 being 16 SIMMS)