I'm not familiar with used architectural patterns to add new feature to an existing set of smart contracts. Contracts can be upgraded with certain architectural patterns, so perhaps that is used to add new functionality.
Another option is real versioning: for example in Uniswap. Uniswap created version V1 of its contracts, noticed that things work and found ...
Have a look at candidate 3 over here. Concurrency patterns for account nonce
This is a pretty important issue for any account that sends a lot of transactions since one underpriced transaction blocks all transactions that follow it.
In any such case, monitor confirmation and have a plan to resolve any stuck transactions.
Hope it helps.