RWS Stanley's Regauging

Quick question regarding Stanley in the RWS: I've seen the notion around in several places that Stanley derailed because he was improperly regauged.

I can't actually find written confirmation of this anywhere that I've looked - it's not in the RWS books that I could tell, and if it's in *Island of Sodor* I've completely missed it (which is very possible). Does anyone know where the idea came from and if it's confirmed or not?

While not new to the RWS, I'm pretty new to the depth of information it has, so I'm no expert at hunting down information. Also not looking to start any arguments about the character - just curious if there's for-sure confirmation that Stanley was regauged incorrectly/where the idea came from.