I second all John has said, and the matter of the engraved line thickness really depends on the tool used.
Michael Harris was a very accomplished engraver before he took up with hot glass seriously, he was able to use a diamond point pen effectively, or whatever tool they happened to have available at the time.
Earlier on, they hadn't got around to introducing standardised finishes or having everything identifiable from catalogues in neat little spreadsheets.
The coach-bolt pontil scar finish literally appeared because there just happened to be a coach bolt lying around handy at the time.