Thanks, Phil.
I was looking at one of my albums and it occurred to me that this stamp Panama Scott# 256 is the only stamp I can think of that was originally issued having already been overprinted. Panama released two stamp issues to celebrate the arrival of Charles Lindbergh to Panama. I think it was the intent that both stamps said, "Homenaje a Lindbergh" or "Homage to Lindbergh" on them. However when the first of these two-stamp series was printed, it turns out they forgot to add that phrase to the stamp, so it was overprinted with these words.
The second stamp issued, the 5 cent value stamp, included the phrase in the design in a box right under the map of Panama (even if it is a little hard to make out).
As a side not this would also be the first visit of Lindbergh to the US Canal Zone. He flew a number of first flight air mail routes from Panama and the Canal Zone.
Covers with cachets were issued for this occasion. One example is below.
re: The only postage stamp issued initially with an overprint?
Thanks, Phil.