Identify new data and display in a table.

[#1]

I have an excel worksheet that contains all of my data.  This data includes:

Account #

As of Date

Customer Name

This worksheet contains data for the past 7 months and contains information about the accounts being worked by the department.

An account can be in the department for years, but month over month, new accounts come into the department and old ones get transferred out.

I need to create a method that will allow the user to pick the "As of Date" from a list box, i.e.

Once the date is selected, I need a table to populate the account data of new accounts by comparing the prior month to the current month.

For example, if I click on the list box "07/30/15", I need it to compare data against the prior month and display new accounts in the table.

I have tried a couple of things:

AcctMap:       

Mapping Load

  [Account #],

  'Exists' as Exists

FROM

  LoanListData.xlsx

  (ooxml, embedded labels, table is [Loan List Data])

Where

  [As of Date]=Date(MonthStart(Today(),'MM/DD/YY'));

FactTable:

Load

  [Customer Name],

  [Account #],

  ApplyMap('AcctMap',[Account #],'Does Not Exist') as Exists

FROM

  LoanListData.xlsx

  (ooxml, embedded labels, table is [Loan List Data]);

This was to identify these accounts by populating a column with "Exists" or "Does Not Exist", then I would filter the data and display "Does Not Exist" accounts in the table.  There has to be another way.

Any ideas?