It's saying 0 matches for "[^13]{2,}".

Doubtless, either:
a) you're not using a *wildcard* Find/Replace; and/or
b) the document is not as you described in your latest attachment.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]

With a “wildcard” Find/Replace, try using “[^13]{2;}” (with semicolon instead of comma).
However, you could still use a standard non-wildcard Find/Replace with:
Find = ^p^p
Replace = ^p
It does work in Word 2007.

It just worked fine. But at the end of the document, serial numbers placement messed up:

As is glaringly obvious in your own screen capture, those last 3 lines (paragraphs) have a left indent. Set it to naught.

That would only be applicable if the OP was getting an error message saying the Find expression was invalid. That is not the case here.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]

Again, show non-printing formatting marks, please.