Originally Posted by Fabo.sk

It's ever slightly more complicated, purely domestic airports do not need neither passport control nor customs, but can not have international flights even from Schengen area. Perhaps flights without baggage interlining.

You can also have international airports with customs but without passport control, which would allow for Schengen connections, but that wouldn't make much sense to build. Perhaps due to staffing, such as non-Schengen terminal area exists, but is not used.

You are correct though that baggage carousels are invariably in such area where there is no segregation between schengen and non-schengen pax.

Plus, there is the added complication of non-Schengen arriving pax might still be arriving from the Community and therefore not subject to customs restrictions