bapu
In an 18 month pay plan you already have paid for 12 months. You have that unlocked working version (as of the 12th month). You are effectively now (month 13) on a new payment plan and stop at 6 months. Implied in the only pay 6 moths scenario is you revert to demo mode.
BUT, since you have an unlocked workable version (albeit 6 months old) you should and would revert to that.
Simples.
So, once again:
I start pay monthly NOW, and you start to pay monthly 6 month later. We both stop in 18 months from now.
By your "simple" logic, you are allowed to keep the latest version (you will just finish your 12 month cycle) while I will be reverted to the old version. ???