Yes, avoid reusing a single-sig key you've used for years in a new multisig setup.

Your public key has been exposed on-chain every time you spent from it, giving attackers a head start if they compromise another signer or break quantum resistance later.

It also links the multisig back to your old addresses and activity, killing privacy.

Mixing it in messes with clean backups, separate seeds, and proper multisig derivation paths.

Best move: create fresh seeds on new hardware, sweep your funds over, and retire the old key.