Mysterious St. Petersburg Postmark

Calling all you cancel experts.
I have what seems a pretty non descript US cover sent from Milford Kansas on March 4 1955 (postmarked on front) to Asheville, NC (postmarked on back March 8 1955).
All well and good, but there's another postmark on the back from St. Petersburg Fla. dated March 10 along with a 1 and at the bottom on the circle ?EN. DEL.



Any thoughts why it would have been stamp in a third state two days after delivery to it's destination?
There's also a MAR 20 ??1 date stamp on the front, but that's probably some internal, received notation.



Any thoughts?

The Saint Petersburg, FL postmark is stamped "General Delivery" or "Gen. Del." for short. My guess is that the piece was sent from Kansas to North Carolina and the recipient likely moved or was vacationing in Florida and there was a forwarding order on file with the post office to forward all mail to Saint Petersburg for pickup.

Brilliant, wt1. You come through, as usual. And so simple too. Many thanks.