Here's something that's interesting, parts of Squid Baby, which is an HD episode were produced before Hello Bikini Bottom (a 4:3 SD episode):
Here's a model sheet for Squid Baby dated December 9, 2011
View attachment 20316
Here's one for Hello Bikini Bottom which wasn't shipped until March 23rd 2012:
View attachment 20317
That could explain the weird airing order that occurred at the beginning of season 9a/end of season 8, widescreen episodes premiering on the same night as 4:3 episodes. They likely made the season 8 holdovers 4:3 on purpose (despite HD episodes already being produced) to keep them consistent with the rest of the season.
Even Patrick-Man was made before Hello Bikini Bottom:
View attachment 20318
I also saw an article on Facebook about Johnny Knoxville being finished recording his lines for Extreme Spots which was in January 2012. I can't find it but I'll dig it up if I can find it