Well, I might get just lucky :) However, since passport change I did it twice in person, then online, then registered mail. Will see in June if I can do it online again. I will remember to let you know :) (and yes, I have old TM6 from January 2020, with old passport number in it).
But I did it online :) Have new passport since June 2020, did the stamp transfer and 90-days notification in-person then (CW), in September another in-person 90-days. in December 1-year extension and online 90-days. In March I did 90-days by registered mail. And we will see in June :) And didn't leave Thailand since January 2020
I tried eServices application for the first time. I changed my passport last year, already did marriange 1-year extension and 90-days notification (in person, online and by registered mail) with the new passport, but the application still shows my old passport number...
Immigration Division 1 (CW). From their website: "Your new form will be stamped as of the expiration date of your old receipt." I did it two weeks ago and it was exactly like they said - I got precisely 90 days since due date (or maybe it was coincidence).