In Vietnam war repts numbers are used. What do they mean, for example: 2/A/4-12, 291200H, YD157687.?

Question

I got the above numbers from Significant Events reports. I know the middle set of numbers (29th of the month, 1200 hours), but the others....??

Answer 1

2/A/4-12 is 2nd Platoon, Alpha Company, 4th Battalion - 12th Regiment (probably infantry regiment)

291200H is 29th day at 1200 hours (the H is for the time Zone I don't Know what one it is probably Vietnam's)

I have no Idea what the YD number is

Answer 2

I'm sorry, if I told you, I'd have to kill you.