It's more that the opposite would make absolutely no sense.
Thread IDs and User IDs can be found in any post, because someone pointed to the right thread as answer to a question, or pinged an user. If at one point one decided to change those IDs, it would imply the edition of every one of those posts, in order to make the links match the new one...
In late March 2018 (more or less when Sam ended the big changes for the database infrastructure) there were already
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that would have needed to be scanned in order to know if they needed to be edited or not. Way too many works, even considering that it would be automated, and way to many risk of errors.