I agree with Ian and with Inertia too :)
Jtan, Please, try to make one longer post with several questions inside one post.
As to the c1/C2 vs lifespan correlation...
I agree that all else being equal, discs with a higher amount of C1 or C2 errors will probably become unreadable faster than discs with a low number of errors (with the number of discs being compared >=100) in normal daily use.
Please note the definitions "all else being equal" and "normal daily use".
Why? Normal wear/tear induces additional errors on the disc due to scratches and tiny holes, which make the disc have more c1/c2 errors (or actually reading problems with drives which in some cases results in proper c1/c2 errors).
As such, discs with a lower number of errors are less likely to become unreadable as fast as more erroneous disc, when both are handled daily and the number of errors on both kinds of discs goes up due to normal wear and tear.
But, there is no reliable data anywhere that I know of that draws a useful correlation between initial C1/C2 error rate and the lifespan of a disc, if the discs are just stored inside a humidity / temperature / abrasion / radiation controlled environment (i.e. stored properly).
Of course, using plain reasoning it makes sense to start with as good burn as possible (c1/c2 count as an example) when one starts to store discs properly for a long duration.
However, this does not mean that two discs (disc A with higher amount of c1/c2 and disc B with lower) will remain readable under archival conditions so that A dies first.
My personal experiences with Kodak Gold Ultima (reflective layer peeling off), older TDK manufactured disc (reflective layer oxidizing into a see-through sieve) and Fuji discs dye layer being wiped clean by exposure to heat and/or UV have shown that even low number of c1/c2 errors disc can die fast, if the batch is bad or there are other problems with the disc (as Fuji used to have with their earlier dyes).
So, my initial answer (oversimplified) was more of the latter case than the former case: there is no simple correlation to be drawn between initial c1/c2 count of a burned disc and the lifespan of a disc when the discs are handled properly. With normal daily use the bets are more off and a good quality burn can die faster than a bad quality burn (case in example Fuji), so ideally it is best to try and find a disc that has stable dye, very good oxidization/UV protection, excellent scratch protection AND the lowest possible initial C1/C2 count after having been burned.
I hope that clears up my initial blabber :)