Before posting this message I read through all the posts for finding and
counting unique entries and tried most of the responses and still have not
found a solution that works for my situation.

So here goes:

I have a spreadsheet with 700+ entries. The records I need to sort on look
like this:
CMMI2_CM_GP2_08_G
CMMI2_CM_GP2_09_P
CMMI2_CM_GP2_09_P
CMMI2_CM_GP2_09_P_PD_PP_H
CMMI2_CM_GP2_10_P_ND_PP_H

In the example above the duplicates are
CMMI2_CM_GP2_09_P
CMMI2_CM_GP2_09_P
CMMI2_CM_GP2_09_P_PD_PP_H

So when I've tried using Advanced Filter, the two that look exactly the same
are filtered out, but the one with the "PD_PP_H" extension is not.

[No, that extension cannot be filtered out ahead of time and yes, it is
important to the data set].

Now what? Thanks in advance for any suggestions and help.