Try this and share the result .
1. Create Formula variable on Invoice Date field.
2. Create a formula as NODIM ( '99991231' - FORMULA_VAR )
3. Create condition on this new Formula . to take TOP N where N = 1.
Else, write a Customer Exit variable . Which would select distinct dates from your Provider and select only the latest date and then filter with that date in Characteristics restriction.
Cheers
Anindya