I also had the same confusion when I wanted to renew my class 2 regarding this contradictory statements..
finally my class 2 medical officer said its only 12 months if u hv done yr flying in india BUT in case u hv done yr flying abroad it wud be 24 months... as u wud hv also done tht countrys respective medicals..
also u hv 2 options in this situation.. In case yr foreign medical is VALID as CLASS 1 only, u can directly take appointment for indian class 1 based on yr foreign medical, else u can renew indian class 2 and apply for class 1... as usual..