Also doesn't it give the purchase date in your account? I thought it did.
No it gives you a registered date, that should do, count 12 from that.
[edit] it gives you a purchased and registered date on the actual download page
[edit 2] Might even be worth it to gab the very latest stuff, you never know when the release the authorization fix thingy, it may allow you to have any version, I imagine it might take a bit if everyone got a personalized fix that only allowed up to what they owned, but I don't really know, but can't hurt.