Re: Out of tolerance gauge blocks
I don't know that this is "THE" answer. But what I would do is plot the history on the impacted blocks to convince myself whether the readings made statistical sense. If. for example, I had five years at one year intervals, and I saw a general trend, then a "JUMP" in the readings, that would personally be a red flag to me.
If you just switched vendors (i.e.: the blocks have previously been cal'd elsewhere), that may be a potential red flag.
If you have any instruments accurate enough and adequate resolution to reasonably resolve the shift, try some experimental readings to see if they correlate.
These are just some checkpoints I would do.
If you discern that your experimental readings don't correlate to the illedged shift, that is another red flag.
If these are critical or important, I might suggest sending them blindly to a different TRUSTED vendor, and have them re-calibrated. Compare the readings (to within uncertainties).
I'm not at all an expert with gage blocks. But there are a number of reasons their readings could be skewed.
There numerous "if this then that" options too lengthy for this post. Hopefully the above will give you some options and ideas.