1) I've failed using BNO as epassport in FRA
2) I've only made to use the nonEU desk once in EU (out of 6 passages (2013-2015)). TBH that time i went off JL F so was first to immigrations. never had problems when approaching the EU desks at FRA (3 times) and CDG (2 times). never other ports.
3) I've used BNO at LCY using the UK lane. got told off but neednt requeue.

based on 1); I'd say we couldnt have used the EU line within EU (I dont think a german system would be miscoded - the BNO one might, i should have tried in france too). However, 99% of the time they dont give a crap