For those confused like me: the line drawing shows both halves of the stela, including the ‘7’ (-..) just above the break. The bottom half was found 30 years before the top.

Im still unclear how they determined the constant to convert from long mesoamerican to GMT. What common reference event could allow syncing these calendars to a +/- 3 day precision? I would guess some solar eclipse pattern visible from both sides of the Atlantic?

Okay, my fault for skipping a lot of stuff in the middle, but a question began to burn in my mind. They have determined the full inscription, calculated the Olmec date, and correlated it to our Gregorian reckoning. The end of the article says:

  So, while 32 BC seemed awfully early for the Olmecs to carve this stone, there’s no way they could have done it later. (Or earlier, for that matter.)

But I am not sure if this resolves the burning question: what makes everyone believe that the inscription corresponded to the current date? Certainly, that is a common custom when erecting a monument, but what if Olmec logic said "let us commemorate this auspicious event that occurred 300 years ago!" or "Let us anticipate the far future in 5,000 years from now!" for example.