Discussion on this curious 1950 RB-150 is at this Banjo Hangout link.
From the conversation:
The serial number on this banjo’s pot is 6510-23. Banjophiles identifies it as a Gibson 1950 RB-150 with an arch top tone ring, which it has. It also has a bow tie neck, with a bound peg head, and a blank Mastertone finger board block.
My banjo also has a Presto tailpiece and a chrome armrest, both of which appear newer than the rest of the banjo.
Yes, the FON is lower down and not close to the tone ring. However, the FON isn’t on the wrong side. Check out earnestbanjo.com rb-150 #6481-77. If one holds my banjo, as he does in picture 12, the numbers are on the same size relative to the neck. I will look at other bow ties from the 50s, but think mine shows the number correctly. No dispute on the anomalies, however. They weren’t as critical an issue then like now.