Back when I started following Deino on Twitter, he had recently posted about total Y-20A numbers and I have taken note every time he updates ever since. I didn't realize all of the tankers had been concentrated in the 38th regiment, while the Y-20s are in the 12th and 37th.
My count is at 92 Y-20As in total, which would mean 46 aircraft per regiment. This seems pretty big though. Did I completely lose track, or have some regiments been filled up with more aircraft than authorized strength in recent years?
I recently learned that air regiments tend to consist of three groups with 8 or 10 aircraft each. I also saw a conversation in the J-20 thread speculating about regiment size, and the two possible numbers mentioned were 24 and 30, so that tracks.
If there are indeed roughly 90~ Y-20As, the rumor the 39th AR has received them might make sense. But apparently there is some discrepancy in the serial number of the alleged 39th AR aircraft.
It also may not be out of the question that a regiment could be much bigger than normal. If the PLAAF has a big requirement for transports but can't really afford to build more airbases or convert existing ones to transport duties, it would make sense to just make an existing regiment bigger. In addition, currently all transport regiments are located in the WTC or CTC, in other words far out of range of sea or ground-launched Tomahawks. Although the coastal theater commands might require their own heavy transport aircraft, stationing them in those areas would put them at risk of destruction. If H-6s are lost to such strikes, their role can be filled by surviving (more survivable) assets like road-mobile ballistic missiles, ships, subs, etc. But heavy transport aircraft cannot be replaced easily.
Therefore transport regiments would need to be expanded to a much bigger size than combat air regiments because they would be tasked with serving both the theater command they are based in as well as theater commands that lack heavy transports due to their vulnerability (or at least hypothetical vulnerability) to enemy strikes if based there.
EDIT- To be clear, when I say all transport regiments are in the WTC and CTC, I mean dedicated transport regiments, not the SAR & Transport regiments, the transports of which I assume have a utility role and are too few in number to meet the transport demands of a major conflict.