[mybestbretts]

This is just my opinion. For the purpose of collecting I would use
the one year. You might go to PSA registry master set and see what
they use for the years of the different postcards.
I have done some study on this and here is what I know.
Most "postcards" were used by teams for various purposes. Many
were provided to newspapers or giveaway at the park and were
probably used over a period of time. For the purpose of collecting
they are called postcards. With the Brett's there is one year (don't recall
which right now) where his auto is stamped on some. I think those
were given to members of the Brett fan club but don't really have
any varification. The royals didn't really keep track of any of that at
that time. Hope this helps