Yes, absolutely: here is a postmark made in Dallas showing postal zone 32:
It just might be the postal zone --would make sense.
[Dallas 32, Tex back then] now 75232 was Oswald's neighborhood coincidentally.
I looked around a bit and saw Dallas. Texas. 5 [would be maybe the Highland Park zone] here---
Here is a Dallas Texas 7 post mark...would be 75207 perhaps? The Riverfront area---
A lot of 50's and 60's Dallas post marks don't have any zips, zones or extra numbers.
And then some others [I could not copy] do have 1A or 1B. Who knows what that means?
But it actually should be written Dallas 32, Texas to mean a zone. It could be [as mentioned] a 2B upside down-- terrible printing though.
Currently, all mail cancellations are made up near Coppell Tx [DFW airport] and zips are not even used anymore.