Election Commission introduced VVPAT machines that print a physical copy of the vote with the symbol you chose to vote and will drop it into a box. (Through a glass screen, you can see your vote being printed and dropped into a box).
When the Electronic Voting Machine (EVM) result count is challenged, the VVPAT votes box is supposed to be used for physical counting of the votes in that polling station or constituency.
My prediction is that the Election Commission of India didn't think through this thoroughly.
The printers used are thermal printers. (Like the receipts you get on a thin paper with black ink at Big Bazaar, KFC and most other retail outlets). As you might have noticed yourself, these receipts fade out by themselves, even if untouched, in 10 to 30 days, depending on the quality of the ink used in the thermal printer.
The first poll date and the counting date are more than 40 days apart.
I suspect that when the election commission opens the VVPAT boxes for recounting, they might just find empty white slips with no symbol.