did a bit of research on these for ya...looks like they generally are early test yield chips that passed and were put into production.
https://en.wikipedia.org/wiki/Engineering_sample
Note, from what I have read SOME of the earlier ones came unlocked for those that like to overclock (back when that even meant something...not really something you do today LOL). Some also had some flaws like power consumption (too much) etc that were fixed before production. You probably got some that passed, so they were used most likely.
Might be something a collector might want to have...especially if one of the older P4 (single cores) like I mentioned above with the unlocked multiplier.
Always cool to find interesting stuff like that.
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