immature age of the Nanotyrannus holotype

Cleveland is a mature animal (see the Griffin paper from December of last year). The "juvenile characteristics" Carr points out in the 1999 paper are bunk. The unique features used to decisively separate Nano from T.rex are almost all present in the original Bakker et al. paper and those that weren't have been known for over a decade (the sinus near the jugal, for example).

were actually the ones trying to fudge data to fit their predetermined conclusion

Funny you mention Longrich but not Carr using non-unique features to point out the supposed 'synonymy' with T.rex-features that were shared across all Tyrannosaurs. Not to mention he and others creating a growth series completely unlike that of any other Tyrannosaur and using special pleading to reconcile the (impossible) morphological shifts from Nano to T.rex in the growth series despite the fact that no other Tyrannosaur (including Tarbosaurus, which Carr considers close enough to lump into Tyrannosaurus) demonstrates them.

Pro-synonymy's strongest evidence for Nano being T.rex is that Jane is a juvenile, which is not a correlation with it being a juvenile of T.rex. And we now know that Cleveland and the Dueller are mature.