Can someone please explain watchmaker service mark interpretation?

[HorologyHead]

H Watch Repairers—is there is a ‘standard format’ for the service marks or codes lightly engraved inside cases of pocket watches or wristwatches?  
Sometimes I can see there might be a reference to year/ month but other times am confused.
I’ve included an image of the rear of a 1951 Hamilton 992B Railroad pocket watch as an example.

Thank you for all information you can give, Mike

[RichardHarris123]

Pretty sure the marks aren't standardised, each repairer having their own code.

[JohnR725]

1 hour ago, HorologyHead said:

H Watch Repairers—is there is a ‘standard format’ for the service marks or codes lightly engraved inside cases of pocket watches or wristwatches?

for the most part no. Each individual watchmaker and/or shop had their own system. One of the shops I worked at basically had a reference to a page number in a book. then there are some shops that do no markings at all as they keep their records on a computer and they don't have to mark the watch.

Usually if somebody is marking and they've service the watch before you'll see those next to each other.

then as far as anything resembling a standard goes at one time the American watch and clockmakers Institute assigned all of their members a number. but that was a very long time ago and I doubt that they are using it anymore.

[Waggy]

All I do is use a fine marker (sharpie) to put the service date on the back cover, this way it can be removed with some IPA and does no permanent damage to the watch. I'm in two minds about the whole service marking thing, sometimes it's good/bad to see the markings on the watch case back as you know it's been worked on and vice versa. However, if I took my car in for a service and the mechanic scratched some code into the housing of my engine I wouldn't be too impressed. Hence, I think my sharpie solution is a reasonable compromise.

[oldhippy]

I never marked any of my repairs. I kept a book with all details. These days use Excel or Access and build your own. As Richard said repairs have their own code, some include the repair number some use their cost code.