The 12 hours 2 years bit is the currency requirements for the SEP(land) rating. It is valid for 2 years and can be revalidated by experience, namely with 12 hours PIC experience in the second year and 1 hour flown with an instructor. Alternatively if not meeting the 12 hours of experience, through a single proficiency flight test with an instructor. In the event of the rating lapsing then I believe it's a flight test with an examiner for renewal.
Guys correct me if I am wrong but you do not need 12 hours PIC. You only need 6, the other 6 can be dual. Also you cannot renew your rating with an instructor by a proficiency check, if you choose you renew by doing an LPC, it must be with an examiner. The hour with an instructor is a mandatory flight, and must not be confused with a test.
Cheers.