Trevor Ward, a writer for New Dawn Magazine, just sent me the following email.
It is noted that the code is claimed to add to 19683 but no-one seems to know what the end date is or for that matter the start date. It doesn’t need to because I believe the numbers represent 1/2 the precessional cycle of 25920 years.
The reason is that 1x9x6x8 = 432 an ancient time number x 3 = 1296 a harmonic of the precessional cycle. Note that 25920/1296 = 20
of which there are 20 outer roundels (5×4) in the pavement. The precessional cycle is well known to members of the Craft.