Aside from Cannon Companion and Shadowbeat, were there any other sourcebooks with sections on simsense, skillchips, BTLs and the like? I could have sworn there was more material floating around in one of the books, and I've gone through my collection, but can't seem to find anything else. Am I completely misremembering, or should I start checking under couch cushions...?

The 1st Edition adventure module dreamchipper had information on the very first persona fix BTL chips

Yeah, but I could have sworn there was another, more recent sourcebook that had a section on it.

It could just be that I'm remembering the stuff in Canon Companion, mebbe...

Cannon Companion has the most recent set of rules relating to them. Sprawl Survival Guide, iirc, also has some material about BTLs and simsense and how they relate to the common person.

Well, if you want to be technical, there's also Matrix and Rigger 3, given that the Matrix and rigging are done using simsense.