Hey, just popped on to see how it's going. Do you think some of the behaviour could be birthday related, with the added sleep complexities? R's behaviour changed around May, before his 3rd Birthday, we had seemingly missed the terrible twos, but he's definitely more of a challenge now, I call him my threenager!
We're winging sleep here too, so he's had a cold and been more tired and even told me he is tired, which is unheard of he's very spirited and touchy. So I've allowed a nap some days but early in the day as in pre 1.30pm no more than 45 mins and we had some good nights, then he was at pre-school yesterday so no nap and had swimming, we were too late with bedtime even though it was only 6:45pm, he refused stories and wanted to go straight to sleep, again unheard of, you would think he would be exhausted, but woke and got out of bed at 8, 11:30, 1:55, 4:30 and woke for the day at 6:40, so pretty much like a new born. I can so relate to what you say about friends children, there is no one that I know who's kids sleep is so complex and has these issues, but you're not alone.
Looking at his sleep he's generally getting 12 hrs, I think you're right to fix BT at 6:30 and just keep with it for a few weeks, and throw in the short CN if you think it will help.