re: calculating the 12-month validity period of medical cert. ---> http://www.cic.gc.ca/english/resources/tools/medic/assess/index.asp
http://www.cic.gc.ca/english/resources/tools/medic/assess/valid.asp (Date Modified: 2013-05-07)
Starting Date for Calculating the 12 Month Validity Period of a Medical Certificate: the last medical assessment on file is the starting date for the 12 month validity of a medical certificate.
Medical certificates for applicants who pass a medical examination in or outside Canada are valid for twelve months from the date of the last medical assessment of an applicant's file by a medical officer and/or delegated staff.
in my humble interpretation, yng pinakahuling medical assessment na nasa file mo (in CEM's database) yon yng basis nila. kng wala kang pahabol na med or re-med yng last med.mo na nasa database nila ang start ng 12-month count. if may pahabol/re-med ka, yon yng magiging last medical on file mo.
this explains a lot sa cases ng mga buntis, na huli yng x-ray, na yng date of x-ray nagiging last med. validity on file sa database ng CEM.
kaya, sa timeline ng CEM (14 months), somehow, parang may advantage yng may mga pahabol na meds kc nakokonsider xa as last med on file.