The first real test of the validity of the information will be whether Huangpu Hull 5 puts on pennant no. 538, because that will be such an obvious break with previous numbering patterns.
They seem to be unconcerned by the fact that pt.no. 538 has been used before (like 546), no doubt due to the fact that these JIANGHU’s were more or less immediately handed over to the Egyptian Navy.
Not really, they are just speculating which one will go to which fleet. The online Chinese posters are just putting these things out there based on their estimations. We've known about 548, 549 as the numbers for the 4th pair of 054A for months now. 538 and 550 could very well be the next pair, but we will have to wait and see. I've seen enough Chinese bbs posting to know to not get too far ahead of myself.
btw, thus far, they have not seen a 6th 054A hiding in the back at HP shipyard, so it doesn't support that claim of 6th pair as 546 and 547 will come out with this batch of engines. In fact, the 12 set of engines also include the original 2 054s, so it would make more sense for this batch of engines lasting until 5th pair is finished.