My anecdotal experience would corroborate; last year I added my wife for the first time to my yellow book in Samui, and it took 3 visits over two months, with interviews scheduled out a few weeks.

Recently I moved her to my house in Nonthaburi and because my Thai is not great the lady at the Amphur thought I was trying to add my wife for the first time, and not move her. When she saw the documents we had she said we had everything but asked if she could take copies and have us come back tomorrow because it would take some time.

When she realized it was just a “move wife’s name” and not an “add wife’s name” it took five minutes, but even adding her name seemed like it would have been much different/quicker than where we did it.

Admittedly didn’t go through the process, but left with the thought of “oh, if I had done it here it would have taken days instead of months” 😅 Both places were lovely either way.