Addresses
if someone sends bitcoin to my old address, does that get lost
Addresses never expire. Money can be sent to them more than once although this affects your privacy.
Most wallets generate a new address for each transaction. They do this to protect your financial privacy. This isn't a case of your wallet address changing, it is a case of the wallet creating an additional address each time you indicate you want to receive money from someone. So nowadays there isn't a wallet-address as such because wallets have many addresses, not just one.
Wallet-IDs
What is the significance of the wallet id
Wallet-ID is not a general Bitcoin data item, it is not used in the Bitcoin network and is not used by mainstream wallets. So far as I know wallet-ID is only used by one commercial business, the one that operated the blockchain.info website that I think has been replaced by the blockchain.com website.
So Wallet-ID is proprietary and not anything to do with the Bitcoin network or the original design of Bitcoin or most Bitcoin wallets.
According to https://www.blockchain.com/learning-portal/wallet-faq
To log into your wallet you need your Wallet ID, your password, and any two-factor authentication that you have enabled. Your Wallet ID is a string of random letters and numbers that acts as a username. You can find it by navigating to the ‘General’ section of your Settings menu. Although it looks similar to an address, your Wallet ID cannot be used to send or request funds.
Wallet deletion
can't recall if I deleted wallets and recreated them.
If you deleted any normal, non-custodial, wallet, all money in the deleted wallet is lost when you deleted it. More exactly, you deleted the secret number that is stored in the wallet and which is needed when spending money. You deleted the secret number that gave you control over money.
With a normal wallet you would be able to recreate the deleted wallet from one of your regular wallet backups or from the recovery-phrase (AKA seed-phrase) you wrote down on paper (or stamped into metal) and stored in a fire-proof safe in a relative's house or similar locations. That way you recover control over money in the deleted wallet.
With a custodial wallet, you are completely dependent on what your chosen custodian is willing to do.
