Maintenance Amount and Flat possession

Dear Experts, Our's is Pune based registered Apartment Association under MAOA and we have completed 2 years after possession started from April 2014. First time, builder has collected maintenance amount for initial two years. Some of the owners have taken possession after 6 months, 1 year and even after 2 years since possession activity announced by Builder. We have started maintenance collection for next Financial year starting from April 16 and sent demand letters to owners. Now, owners are telling that, Two (2) years are not completed for us since we have taken the possession. So we will give the maintenance amount only after completion of two years. My question is when maintenance will start ? From the date of Completion Certificate received by Builder or when the owner has taken the possession (possession date) ? Maintenance Amount receipt given by builder doesn't have the dates (period) mentioned when maintenance have started. What if somebody will not take possession for 5 years or worst case even 10 years. What Association can do in this case ? Please guide. Rajan