They have individual cellos? If so:
- Smoking in the next week to 3 months - cello Off
- Smoking in the next 3 months to year - doesn't make a difference whether you leave it on or off, it'll still breathe
- Smoking in the next year+ - leave the cello on and you may get a nice yellow cello in a few years time
You don't need to age NC's, but if you do, do it in a cello.