Probably just an earlier production run. There were a lot of "prototypes" of F14, though. A few clues I remember off the top of my head were the ROMs on the MPU have stickers on them saying "proto" (mine has these). Also, they will have wiring to the flash bulbs that were originally under the domes near the top right loop. Mine had the wiring, but it had been cut, presumably at the factory after realizing it presented a risk of shorting the MPU.
The clear domes you pointed out, as well as a clear center beacon, are from early production runs as far as I know.