yes you are right as many people has been converted either to preview offer or welcome offer but mine is neither in preview or in welcome so i can recharge as many time as i want i am getting recharge button along with usage i have recharge my app also so i am getting longer validity and my validity is valid after 31st december also and my jio drive has validity of 2036 for 20 years and some app are valid till may 2017 and some app are valid till sept 2017.
its a sim.....but to save battery of my phone i have putted a sim in jiofi and my jiofi sim is in preview offer but in this sim i am not on preview nor on welcome don't know why but i am using this jio sim from jan 2016 may be they have not shifted the existing customer as you see my base validity is jan 2036.