Water resistance was a major goal of many brands, and to that end there were companies that would get specially designed cases from manufacturers they didn't normally use. Borgel is such a casemaker, and many years ago I saw a Bulova in a Borgel case. It was a "Swing Ring" case with the FB trademark, and it was shown to me by an enthusiastic Borgel collector in Toronto.
It is possible that there are unknown and small quantities of watches out there that do not conform but are legitimate- they represent an experiment of sorts by Bulova. Many other brands did this, including Rolex, who also issued a quantity of Borgel cased watches before the development of the Oyster case. The earliest of these cases is from 1905.
I've seen a few very unusual Bulovas, (I have one here in the DB that is a hermetic type compressor case, very fiddly and possibly a Surfmaster) and it would not surprise me if like many other companies, Bulova had brief flirtations with other case makers and case designs. Just speculation at this point.