Pray tell what my "lot of assumptions" are. Tesla does its own testing. You can clearly see this within the documents they submit to the EPA.
I don't know which "last delay" you're referring to. But the current one appears to be because the Model S LR has not yet been issued a certificate of conformity (and same for the Model Y Performance). As I noted in the post you quoted, I suspect it's because there is a discrepancy somewhere that the EPA isn't letting Tesla get away with. Perhaps that is one of the assumptions you are referring to - but note that I never claimed definitively that is what happened. I postulated what I suspect the reason to be.
You perhaps have a much more charitable view of the company than I do. But I think history has shown this company and its leadership have no qualms about being dishonest if it helps their bottom line. In this case it seems to have bitten them in the ass for once.
If the other "assumption" is that Tesla didn't do their due diligence and try to take care of this early... I mean that's simply fact. You can verify with the EPA itself when the documents were submitted. Most were in December. Some not until after the New Year. Had they planned earlier, they could have avoided this situation where they don't have a valid certificate of conformity for cars they are trying to sell. They could have submitted the testing as early as Summer 2022 (when the changes were announced) for MY2022 or 1/1/2023 for either MY2023 or 2024.
We can speculate as to why they decided to wait. My assumption would be that Tesla wanted to delay the reduced ranges becoming public knowledge for as long as possible.