This Bulova has a case date of M0 and a movement date of L9. It matches a 1959 Princeton "B" that member RGB has posted. The back of the case has: 10KRolled Gold Plate BULOVA M0 The case, back , crystal and dial seem to be in excellent shape. The watch is running and keeping good time. Buckskinner
How did we decide the "B"? The Fall 1961 Bulova Model price lists includes the following Princeton variants.
There's this 1959 Princeton ad below, but based on the before-tradein-price it's either an A or B and not stated as such/which. I can't tell which from this ad.
OldTickers 1959 example is still ID'ed as Princeton w/o variant designation, and I don't see how to determine variant from that thread.
Is there an ad I didn't see? Enlighten me folks-please
EDIT: I can't find GVP's Princeton B in database as ID'ed record. I think he placed some pics of a similar watch in OldTickers thread and proposed it was a "B".
OK- Based on the price lists, the generic Princeton came out in the "new watches" section of the Spring 1955 model lists. It was yellow gold case (Y). 
The A and B don't appear until the Fall 1958 lists. They appear in the "new watches" section. When watches are listed in this "new" section, they sometimes give more information on gold color, dial color, etc... which doesn't appear in the later lists when they are no longer listed in the "new" section.
The "B" is white case color (W) w/ black dial (blk). The A is yellow case color.
As noted in previous comment above, all three watches still appear in the "currnet models" section in both the Fall 1961 and Spring 1964 lists.
I agree, subject watch is "B" vairant.
In reply to Nice, thorough research on by bobbee
Thanks, but its not near as nice/clean as a few vintage ads.....its more like solid crystal specs until we get ads.
One issue is the unique Bulova model numbers changed format sometime between 1958 and 1961. The '61 list has one section with the "old numbers and new numbers" for cross reference. The Princeton A and B have these different unique numbers in later lists, and we are missing the year when they old numbers were cross-referenced to the newer numbers.