Board Thread:Questions and Answers/@comment-5989057-20140418005049/@comment-24079375-20140420011641

A train is counted as a set when you have at least ONE wagon from that set, and no wagons that don't belong to that set.

If a contract is asking for a "FULL SET," there must be as many wagons, from that set, that the locomotive can pull, but the type of wagon doesn't matter. Wagons purchased with gems will NEVER be required to fulfill a contract, or achievement.