Well, we do need to decide what's the intended behavior.
Of course. That shouldn't take long.
The Bulgarian Empire certainly never existed as an empire in the proper sense (heir to Rome), but their territory shouldn't be considered dejure Byzantine when they exist.
This would be the only possible point of contention. Either the ERE gets that territory de jure in 867, which is the same territory they start with in 1066 and 867 vanilla, or no empire gets it.
So it might make some sense to simply have their territory not belong to any dejure empire in NAE, but that might also break some of the Bulgarian Revolt events.
What other de jure empire is their territory going to belong to in NAE? The HRE is a thousand miles away. It's either none and risk Bulgarian Uprising side-effects (for which I am a relatively poor reference, since you write them) or go with vanilla and don't break any of our events.
I was initially thinking vanilla made the most sense, but given that you've done enough research on the history to actually write the events whereas I have not, I'd then prefer to take your word on it and diverge from vanilla / our own 1066 boundaries if it's more historically accurate for 867 and risk breaking some events, the effects of which aren't as relevant in NAE anyway. Unless those events initiate a de jure claim war or something, I don't think much would change. The Bulgarian Empire is titular in 1066, our primary balancing point, and making it as such in 867 by event before unpausing (keep in mind that the history effects will take place while the empire is still de jure too) will only simulate starting with the two titles' state resembling 1066 (chief difference being that the ERE won't be de jure liege to that land either-- minor).
In any case, that's why I said the change might be as late as tomorrow. I need to either collect pointers from you on what you've scripted regarding the uprising (if something big is going to break if that kingdom's dejure_liege = 0, honestly, you'd remember) or find them myself in the code before making the change with either available option.
EDIT: Further discussion to Skype.