Even back before XP, install CD's are usually set to
only work with a set range of "Product Keys".

No issue of install CD works with all Product Keys.

Each issue works with some select range of them.

AND even if you have a CD/Key that do work together,
they might NOT work with hardware they were not
originally designed for.

Some OEM versions look for their brand of
computer hardware, but some do not.

If you bought an XP CD/License COA/Key from
TigerDirect or some other seller, they got
locked to the first hardware somebody installed
them on.

The CD's and COA Keys Microsoft sold to
"official refurbishers" may have some
additional quirks that I don't know about
but I'm assuming those were similarly locked
to the INDIVIDUAL COMPUTER, not just the
type of hardware they were set up on.

I'm actually quite happy with my fleet
of 6 (so far) identical "off lease" Dell
computers. I got the original CD's and
I can move any bootable drive around from
machine to machine, as convenient.

These same machines sell with "official refurbisher" CD's
but I expected those would NOT allow me to move
any bootable drive around among identical hardware.

No, I never enter or use the ProductKey from the
COA stickers, because if I did, then that install
would be locked to that individual computer forever.

The install CD's use a built in Product Key that
is generic to all 6 computers, it doesn't ask me
for a product key anywhere in the install process.

I WANTED that kind of interchangeable situation, very much.
More than just a model, since there are at least
6 models of main board in this model, I specify
the model of mainboard to match my fleet.

The short of it is that you really need the proper
install CD for the two computers you're having
trouble with, AND since you said you don't like
OEM's, THAT characteristic means that each
install is locked tightly to that individual machine
and so bootable drives can NOT be swapped
around among your desktop computers.

Why is it again that you are so dead set
against OEM computers?