Flight arrangements.

I don't know what flight arrangements Tauck is offering, but there are a lot of options with only 1 stop each way from the east coast (JFK) and one non-stop return.

If you want to fly on one airline for as much of the trip as possible, Delta flies non-stop (both ways) between JFK and VCE so you could purchase a Delta r/t JFK - VCE - JFK ticket then book a separate flight from Venice to Dubrovnik. It might be easier with more options, however, to get into Dubrovnic or have shorter layover via other feeder airports, e.g. Delta JFK - ZRH (return Delta VCE - JFK), and Croatia Airlines from Zurich to Dubrovnik. If you don't mind mixing it up then there are plenty of other options to get into Dubrovnik. A lot depends on what is more important to you, cheaper flight or shorter enroute time, and what time you want to travel. We generally go for shortest, fewest stops, most direct flights.

Travelocity shows Delta with the only non-stop/shortest enroute time from VCE to JFK. We flew back from Classic Italy (VCE to JFK) on Delta. We check with Tauck first, but usually book flights ourselves at the earliest possible date (as much as 330 days out) to get the best Business Class fares, however, we booked our latest trip, Romantic Germany which departs 8/19/2017, just two months ago and Tauck beat anything I could get by a substantial amount (for the same Delta Business Class flights I had been looking at!).