So if I increased the gap limit and used all those extra addresses, then restored the wallet afresh, those extra addresses would not show. Would electrum be able to spend from them or only once I increased the gap limit.to let electrum know about them.
It depends.
As I already said, the default gap limit on electrum is 20. If you have used the 21st address without using the first 20 addresses, electrum wouldn't show the transaction history of the address 21, unless you increase the gap limit.
Electrum starts from the first address, checks the transaction history of your addresses one by one and it stops once it sees 20 consecutive unused addresses.
Take note that your seed phrase generates numerous addresses and it's impossible for electrum to check them all.