No, in 2010 they already used the separate 4 number code. Like they did on this tyre that has a production date of the 38th week of 2011: And it looks like it says 291D instead of 2910 on that tyre.
No, before 2000 the used 1 single number for the year, that makes it even harder to figure out if it's 1971, 1981 or 1991.
No. I have tires now that are new that have one long number with no separation. I'm guessing what you're googling isn't hard fact. It may be a "D", hard to tell.
Thank you all for the replies. I'm thinking a production date 1991. 2 will be out in trunks as spares for emergency use only.