They must have went to Xi'an, because AFAIK:
-16th AB used to field J-11As, but upgraded to J-11Bs in spring 2021 (these aircraft, in turn, came from the 111th AB and thereafter received the "BG" AESA upgrade).
-18th AB then received the 16th AB's old J-11As to replace its J-7s. The brigade still uses J-11As today.
That may be indeed correct. As I said, I don't know for sure off the top of my head right now... but AFAIK we don't have any photo evidence (serial number) for either the 16th or 18th that they are actually flying J-11. Especially for Yinchuan/West (16th AB) there are also indications that they are flying J-10C or even J-11BG too.