having some trouble understanding what is causing the following...

i have a report that we run monthly, each month the results of the report
are pasted in an excel spreadsheet that contains all the prior months
(appended each month so as to maintain a running total).

when i went to refresh the pivot table that summarizes the report data after
adding november data, values duplicated. i found that for whatever reason,
november's data was not being viewed the same as the months prior.

if i go into the raw data and do a control find for one of the november
values, it will only return values from november, even though there are
values in previous months that are the same.

i tried using the len function to see if there was a difference in character
length, but the result was 5 for all values.

text to columns did not work, nor did =left(a2,5)

however, left(a2,4) appeared to correct the issue.

any ideas on why a 4 in the left function would correct the problem as
opposed to 5 or text to columns?