When those first 20 addresses are used, Electrum generates the next batch of 20 addresses, and so on.
This is not true. It's not that electrum generates new addresses after all first 20 addresses are used.
Electrum generates the 21st address once you use the first address, the 22nd address, once you use the second address and so on.
So true. I checked my android wallet today and have extra addresses despite not using all of them.