In those estimations, the difference is more than a few! Several rechargeable battery manufacturers stay on 500 while others ensure 1000 or more. So, when the battery reaches that quantity, does it magically disappear?
Sadly in this case the user could be having incomplete specifications that the manufacturer shouldn't provide, but accurate ones like the percentage of charge after a number of charging cycles. For instance:
84% after 4000 charge-discharge cycles
That was the case of some rechargeable battery using La, Nd, Ni, Co and Si, in the late eighties, and it was not bad at all.
It really happens in this manner, the battery loses some capacity although the working principle continues providing benefits to users, avoiding multiple issues to the environment.
According to different sources, for Ni-MH and Li-Ion, the most widely used type of rechargeable batteries nowadays, it's 500-2000 and 400-1200 charge cycles respectively.
Is it possible that a technology with almost twenty years clearly outperforms the standards of today? There's a long road ahead for technology, and this field is no exception.