When something goes wonky with a CMM, it's usually fairly obvious in my experience... loss of focus (Z-axis motor), clicks, grinds, absurd data coming out...
If you're worried about it...simply keep a "known" at the machine and measure it when in doubt.
I had a MicroVu Vertex for 13years of daily use and the only time it needed repair for function was when a z-axis motor went out...it was pretty darned obvious with all the racket it made trying to focus.
Measuring 20x on the same part to verify seems like total overkill...just make a simple test regimen (2minutes or less) to verify function.
We had a program to measure ID and OD of O-rings...I just put my wedding ring on the stage and hit "go"...if there were any issue in X, Y or Z it would have shown up immediately. I would do that perhaps 2-3 times a year, typically while training someone new to the machine.
Other operators used it every day, multiple times a day...again, if something were wrong, it's pretty obvious on a CMM.
HTH