-={ 2021-04-13 00:05:42.194992579+00:00 }=-

Hey August!

 AA> And.. if I don't see it, it probably means it was detected as a
 AA> dupe along the way!

Yes.  My money is on 1:153/757 since that system is the first that MSGs from 1:153/7001 will encounter.  For sure the Europoint didn't see it so somewhere along the line it got caught as a dupe ... which of course it wasn't.  It was a perfectly valid and original packed MSG with a duped MSGID which could happen although like you pointed out is highly unlikely to happen in a three year period.

Life is good,
Maurice

... Druncen beorg še ond dollic word.
    Guard against drunkenness and foolish words.
--- GNU bash, version 5.1.4(1)-release (x86_64-motorshed-linux-gnu)