Where is real Delve:

The Imperium knows where Delve is at all times. They know this because they know where it isn't. By subtracting where it is from where it isn't, or where it isn't from where it is (whichever is greater), they obtain a difference, or "deviation". The Imperium uses deviations to generate corrective narrative spins to move real Delve from a position where it is to a position where it isn't, and arriving at a position where it wasn't, it now is. Consequently, the position where Delve is, is now the position that it wasn't, and it follows that the position that it was, is now the position that it isn't.

Yep.