Only theoretically. In practice the only thing that usually matches is from which other ATC unit the plane is coming. But it could be on a different route and will almost always be at a different time due to operational variation.

That doesn't matter, because the previous unit actively hands the plane over. You don't need the flight plan for that.

What does matter is knowing what the plane is planning to do inside your airspace. That's why they're so interested in the UK part of the flight plan. Because if you don't give any other instructions, the plane will follow the filed routing. Making turns on its own, because the departing ATC unit cleared it for that route.

> the previous unit actively hands the plane over. You don't need the flight plan for that.

I thought practically, what's handed over is the CPL (current flight plan), which is essentially the flight plan as filed (FPL) plus any agreed-upon modifications to it?

> Because if you don't give any other instructions, the plane will follow the filed routing. Making turns on its own, because the departing ATC unit cleared it for that route.

Without voice or datalink clearance (i.e. the plane calling the new ATC), would the flight even be allowed to enter a new FIR?