I am not familiar with that particular tool, which makes me the ideal person to ask the obligatory dumb questions first without fear of humiliation.
"spindle may have rotated" - does the contact point thread onto the spindle? Is that the potential source of rotation you're referring to?
Has it seen any impact or other unlikely event that could change the spindle's opinion about where it should seat?
Have you removed the contact point, cleaned everything, and reinstalled it?
"might be off by .02845" - might be or is? How have you arrived at this number, in so many decimal places? Is the gage reading off this much or did you use other tools to decide this?
If the gage is reading off this much, can the gage be re-zeroed?
"The contact point is no longer flush to the base" - if you replace the previous contact point what changes to the device are evident?