That sucks that you haven’t seen any movement, and I honestly thought that you would have seen some by now.
The only thing that I can think of is that it’s related to the particular model that you’re ordering, particularly the amount of memory. I’m thinking that Apple underestimated the demand for the 1 TB and 2 TB versions, and had to produce more, and that people ordering those are seeing the greatest delays, and have less of a chance of being moved ahead of time.
I‘m thinking that the reason that I got “lucky” was because I ordered the 512 GB size, and maybe, Apple made more of those, and was able to bump people up from later dates. It’s also possible that there was more demand for the 128 and 256 GB versions as well, since they were the lowest priced of the 12.9” ones. This is speculation on my part, of course.
Best of luck.