Most of the decorated graves in Billerica's South Burying Ground bear a black-on-clear sticker that says "VETERAN." I'm guessing that someone with a list of veterans' names and a roll of stickers went around looking for gravestones that matched the list. Later, someone else came through to place flags. Unfortunately, it seems that neither person bothered to read the entire epitaphs.
Either that or Billerica was defended with very tiny muskets.