
:D:D
I just got your email, David, it looks as if you and I both thought the same! There's an attenuated bottle, listed in Miller's guide '05, p314, with a broken pontil mark, dated at '73-'74. I shall have to track down the date for the start of the flame pontil mark.
Early stuff had broken pontil marks. They started experimenting with putting a blob of glass over the pontil, the first appropriate thing that came to hand to mark the blob was a coach-bolt with a round head, so there are some early "coach-bolt" pontil marks. I have a couple of these, on "Seaward" pieces. The flame pontil would suggest your date of '75 was pretty accurate, David - I was being more cautious!