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Darks can work for a long time. CCDs generally slowly degrade over time so they may develop columns and extra bad pixels.
CMOS will too but at what rate I don't know but these same CMOS sensors in mirrorless cams redo the bad pixel map once a month. So the fact your digital camera may be clean is because it does this routinely.
I also don't see any CMOS camera suffering from those hot columns that a lot of the KAF series CCD sensors do. But I have used 3 year old darks very occassionally and they worked nicely.
But with CMOS you need multiple darks to match the various settings as that all needs to be exactly the same as your lights.
So I would:
1. Standardise a temperature that can be achieved all year round and the lowest you can reliably achieve.
2. Use only 2 settings for gain, one for regular imaging and one for narrowband.
3. If you are using QHY that would be the readout mode for each type of imaging.
The usual advice for CMOS (not sure about the 16bit sensors) is not to use bias frames and use flat darks when making flats.
Greg.
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