To date, I haven’t been able to discern a pattern. The movement may contains additional letters stamped on the plate of some pieces, which were related to production logistics of the time, and were likely a method to keep track of different batches.
Chronograph bridges stamped ‘400’ were used in later caliber 400 pieces introduced in 1987, and ‘400Z’ for pieces introduced in 1998. Lastly, there are pieces that show either ‘400’ or ‘400Z’, with no text. I do not believe these are original A386 components. As with the above, we find these on the questionable xxxD460 pieces, and others with numerous replacement parts. I am not sure if this is a Zenith component, but at the least I do not believe it was originally used for the A386. 
These we find on the questionable xxxD460 pieces, as well as other pieces that have had a significant number of parts replaced. I see these bridges in a few of the 538Dxxx series (Mk 1), but enough to believe they are correct. ‘ZENITH’, with ‘THIRTY-ONE 31 JEWELS’ and ‘UNADJUSTED’ text below, and then ‘3019’ above ‘PHC’. 
Seen across all three executions, including all 3 of the Mk 3 production batches. ‘ZENITH’, with ‘THIRTY-ONE 31 JEWELS’, and then ‘3019’ above ‘PHC’. On the chronograph bridge we generally see four different sets of text, only two of which I believe are intended for the Zenith A386: Within the A386 family we see a variety of different engravings on the chronograph bridge as well as the plate. 
Zenith compensated for the watch losing power more rapidly due to its high beat by incorporating a mainspring with 50-hour power reserve. Higher frequency brings greater precision, with fewer variations in rate due to external factors. The A386 uses the El Primero 3019 PHC high-beat movement, with 36,000 vibrations per hour (5 hz) permitting measurements to the tenth of a second, which at time of release (1969) compared to the competing Caliber 11 at 19,800 and Seiko 6139 at 21,600, and the standard 18,000 vph (2.5 hz, measuring to a fifth of a second).
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