Export to Excel - some dates (dd-mmm-yyyy) turn negative

I am trialling Adobe Acrobat DC, with a particular interest in exporting tables in pdf documents to Excel to facilitate searching and filtering on the data.

The dates are in the format dd-mmm-yyyy  e.g. 12-Nov-1797.

Many of the dates show up correctly in Excel but just as many are converted to a negative  number which shows up in Excel as a string of #.

In one document, the dates not converting are left justified and those converting correctly are right justified but in another there is no apparent logic.

I have a workaround, exporting to html and then importing the result into Excel.

I tried another product PDFElement (which allows 2 page conversion as a trial) and that converted ok.

I think there is a bug in the Adobe product and probably a fairly simple one, but I have not been able to find any way to report it!