Back in 2015, I arrived from NRT in Istanbul old airport with TK in the morning and wanted to travel the same evening on TK to Germany. I checked my luggage to Istanbul short, since I had to pick up things there. When I wanted to check in my luggage, I was denied to check my luggage in because there were two more flights to the same destination on the same day before my flight.

Seems, that nothing changed in this point.