1. This might be incorrect in YOUR case, reasons escape me. In general, in the art world it is common to appraise at values higher than what could be realised comfortably at the time of the appraisal. There is really absolutely nothing to discuss here... Unless the object has been sold and money is in the bank the appraisal figure remains a fiction albeit a superbly informed one. Notice the huge oscillations at auction for the art segment : sometimes less, many times much more than the appr. value. Why did you think "reserve" has been invented ??
2. Very uncommon does not mean "not at all". It does happen albeit not often and I know of a few cases of "X's instrument is for sale"... I am pretty sure you know, too.
To further clarify : if a violin has been appraised at $nnn and later was found to have been mistakenly attributed etc etc... It seems it happened to the best of them.