It was my understanding that all the 50's had the "ventless" windows and the "pull down" refridgerator door style handle.. a 50 with window vents and a push button door handle would suggest to me that somebody scored some later doors and put them on...
...that was, untill you mentioned that you don't have a cowl vent on the drivers side.. i'd guess that the truck is actually a '51 or later.
How are you determining the year of your truck?
From the Mfg Plate Serial Number (located in the drivers side door jam) or from the date on the title?
Here's an excerpt from the stovebolt TechTips section:
".. some states titled vehicles by the year they were sold, and not the model year. Since production usually started in September of the year preceding the model year, you may see a title for what you would call a '39 truck, but it says '38 on the title. This can happen easily since it was sold in the last part of '38, but was really a '39 truck. Some states called this a '38 then, since it was sold in '38. I've seen this happen up into the early '50's. You may also see one that was a slow mover and got sold a year after it was made, and titled as such."
See if you can get the serial number off your Mfg plate.. if the plate is still there, and the number is still readable, that will be your best bet as to determining the actual year of the truck.