As a long time lurker on this forum, I'd like to thank everyone for their recommendations on the tenore. They're an amazing pair of IEMs for the price, and sound comparable to or better than my other way more expensive IEMs.
I have 2 pairs of tenores, one of which I believe to be reference, and one which is bass heavy. My first pair I received were bass heavy (after comparing to impressions on this thread and my own pair of er4s) so I duly ordered another pair from amazon japan (which was easy since I'm based here). The 2nd pair I received has a much more balanced low end and they sound amazing to me with sony hybrid tips.
I read something regarding wire lengths earlier, and after comparing both pairs, the bass heavy pair has a wire length that is about 3cm longer than the reference pair. This difference is probably due to manufacturing variations from batch to batch, which might explain the variations in bass levels.
That being said, both pairs still sound darn good and I will be keeping both.
So that's the difference I will say. I know if you add cable length to the Tenore, the sound gets bassier and darker, so those batches with the shorter cable are the reference ones. I though it honestly had something to do with the big vent clogging but even blocking it makes little difference. Also, sources with high output impedance will also make them sound bassier and darker.
Bass should only be the thing changing between batches I'll say, I think very likely the rest of the spectrum are pretty much the same between batches.