Dual Crown Super Compressor.
Fifth- I'm not sure what to call the 314 inside. I guess it would be the "case number". The case serial number is on the back and appears to be entered correctly as 355205. - the 5768 seems to be stamped on in a different font than other case back markings. So what does the 5768 designate? Perhaps it is "run" 5768 of case number 314"?. Or it could be unique watch number 5768 of case number 314? Or it could be the case number like Old Ticker says. I didn't help much here, did I?
For the 666ft Bulova watches, there was some required testing by Bulova. The industry-wide depth rating was about 633 ft for this class, but Bulova advertised as 666ft, a little extra.
Now did they test at 666ft?
or guarantee water-proof at 666ft?
or just test and guarantee at the industry-wide rating standard (apx 633ft.) and fudge the extra few feet for for Bulova marketing/advertising? The 666ft signature on the case back may not mean "tested or rated to 666ft"- I'm almost sure it doesn't. But Bulova may have guaranteed them to this depth anyway for marketing.
Also coming into play on subject watch is the "super-compressor" technology licensed to Bulova by Brevet. Over 40 watch manufacturers were licensed to use the Brevet technology around this time (this includes all three versions: compressor; compressor 2; super compressor). One of the stipulations by Brevet to grant use of proprietary technology MAY HAVE BEEN some waterproof guarantee requirements set by Brevet.
On subject watch, the 5768 number could be the "pressure test run" number. ...and not ALL watches in that run may have been tested - just a random sample. Perhaps the watches which were tested in run 5768 had that number stamped on the back, and the other watches which were NOT tested in that run didn't have the number stamped on the back. Mark-This could account for some having the number (5768) and some not having this number. If there were any rhyme or reason to the longer case serial numbers on these watches, Bulova could note the serial number range of watches which fell in depth test run 5768 to monitor unique watches not tested in that particular run.
Example Pic (below) of 1961 watch w/o four digit "depth test run" number on back.