FDC With Two Separate Cancellations

This subject may have been addressed sometime in the history of this forum, but, still being relatively new I am asking.

I have an FDC 42c Alaska Highway with canx 92-05-15 in Dawson Creek, BC; and also 29c Alaska Highway with canx May 30, 1992 in Fairbanks, AK. I assume the envelope was submitted to each P.O. by the owner of both stamps, and that both FDC cancellations are valid, even though the 29c stamp was obviously not a First Day of Issue on May 30, 1992. Request comments. Thanks.

It might be considered a combo FDC in which stamps and postmarks are added that are related to the topic.

These two stamps were issued to commemorate the 50th anniversary of the opening of the Alaska Highway between Canada and the USA.

Both countries issued a stamp, but not on the same date nor the same design.

The Canada stamp (Canada Scott #1413) was released on May 15 while the USA stamp (USA Scott #2635) was issued a couple of weeks later on May 30.

Both of your cancels are first day cancels ... for the respective country.

A "joint" FDC was prepared ... sounds like the one you are asking about.