[Lynn]

From an NCRRS post (at least one typo... 1.1.69 would be half way through the 69 model year):

First use of DOT compliance was 1/1/69 (mid-way through the '68 model year).

From that time to 1971, when DOT standardized the TIN sequence, each mfgr made his own proprietary TIN sequence which contained the source data DOT made mandatory. So, we're essentially 'blind' as to how to decode each mfgr's sequence in this period.

Prior to 1/1/69, the individual mfgrs had their own ID sequences which may or may not have embodied mfgr date information...