Some mobile wallets rotate 10 addresses at random (per unique wallet account) while other wallets generate a brand new address following each transaction. Both options are completely standard, and whether you use one or the other depends on the given wallet and its settings.
These addresses do not expire, you can receive bitcoins to your older addresses just the same, even if your wallet has generated a new one since then.
It’s worthwhile to choose a wallet that generates a new bitcoin address for each transaction, thereby enhancing the security of your privacy. A wallet with this configuration will automatically take care of this for you, with no further action needed on your part.
Because many wallets generate new addresses after each transaction, please make sure to double and triple-check that you’ve given us (or anyone else) the correct bitcoin address. Bitcoin transactions are practically irreversible, so we cannot refund transactions that were sent to the wrong bitcoin address. These transactions are irreversible.