Originally Posted by YYJMSP

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Obviously, if the Aegean segment can't be "added" to the Croatia segment, then the answer to everything is probably "no, you need to get off, get your bags, check-in/drop-off bags, go through security, etc"

I then have a similar scenario/questions for later in the same itinerary, this time coming in off a Swiss segment and going on a side-trip on a non-Star Alliance member (British Airways)...