BoarderCross2000--- You're tires are fine; but yes, that's specifically why the Tire Industry has the codes "encrypted" because they don't want you to know these dates as it might hinder a possible purchase. I do find it odd that 2 were from '07 and 2 were from '09, as most tire shops receive their tires in "batch groups" with very close manufacturing dates.
There could be a very sharp store manager at your tire shop that purposely rotates his stock and always tries to sell the oldest tires in stock first, and routinely puts brand-new inbound tires at the extreme rear of the shelf for longivity. Thus, you could have gotten the very last 2 he had in stock from the '07 batch, and the very first 2 he had from the '09 batch (which were deliberately tucked behind the '07 models on the shelf in date sequence order). Basically; sell the oldest first, and the newest last.