I believe the markings were used back when shooters in DCRA were required to use issued ammo in matches. No other ammo, was to be used in the matches. To easily tell, the ammo was marked with stripes to differentiate it from non match use ammo. I am not sure if the ammo was specifically "match" ammo, or was just a lot set aside for the matches.
If I remember what was told to me, the color and/or number of stripes would change year to year, or maybe by batch (?). this was to keep things even. that was no shooter could, for example, bring in a particularly good batch of ammo that performed better then the current stuff.
These were also usually packed in the ten round paper packets. I was attempting to gather enough of these packets (maybe 30 or so for a 5x6) to have framed for a display, but the damn things keep skyrocketing in price. I didn't get to far...
As mentioned, Gandrite or Smellie would be the resident SMEs here though.