At the least they give you the earliest possible date the bass was produced.
well, again, it only gives an earliest date it was shipped. A bass can be assembled, and left in the factory without hardware... This didn't generally happen with EB0s and EB3s, but the obscure models, later EB0Fs for example often have a weird mix of parts from different years.
I have seen them with '65 pots and '66 pots - so far I have not seen any with '68 or '69 pots - but admittedly I haven't checked that many - Scott did yours have '68 pots?
A big change happened at Gibson in mid-late '66, Stan Rendell took over from Ted McCarty - he changed the Gibson's production system from one in which guitars were simply built, and hopefully sold, to one where guitars were built ONLY when ordered. The first non revs were built before his time - ie without any orders. We all know the stories of unsold Tbirds, so I doubt there were many orders coming in in '68 for them to build more...
It could be that they were all produced in '65 and '66, and slowly shipped, as required, potentially with hardware added in the year they were shipped?
Until a clearly later one comes up it's hard to be sure that there are indeed later ones...