-snip- does the wallet automatic select one of those labeled by received or the wallet generate new address?
Yes, but it can only create up to 20 (
/your gap_limit) unexpired unpaid invoices, further addresses will require you to accept a warning message.
If you accepted it, Electrum will let your generate more receiving addresses despite of the previous 20 being empty.
And uif you're going to rely on the receive tab for new addresses, you must use the invoice's expiration option properly,
If you set it no "
never", Electrum will never reissue that address the next time you generate an invoice unless you delete the invoice.
If you set an expiration, the wallet will reissue the receiving address of the expired invoice next time you request for an address but only if it didn't received bitcoins yet.
Take note that the ones that have expiration are the invoice, not your addresses.
You can still use them regardless of the invoice's state.