Note that the default gap limit in electrum is 20 and that means that electrum gets the transactions history of addresses one by one and it stops when it reaches 20 consecutive unused addresses.
You can ask addresses to increase the gap limit.
If you want to fund your wallet now, use the first address. The next time, use the second address and so on. In this way, there will be no problem in the future.
Ah, now I get how it works. Thank you!
If i need to restore a pair of cold storage wallets from a seed, I first restore the cold wallet on the offline computer to get the master public key, then when I put that into the watching wallet, it checks the address generated until if finds 20 (if that is the gap limit) unused address. I can count these and then generate the necessary addresses in the cold wallet with the console commands.
Cool. Thank you again for your prompt and helpful replies!