It would help to see the data model involved. Layouts are not linked in relationships, Tutorial: What are Table Occurrences? are linked in relationships and each of your layouts are based on a table occurrence selected in "Show Records From" listed in Layout setup. These might be two occurrences of the same data source table or two separate tables.
My guess is that you have separate data source tables and that could easily be a less than optimum design for your data model. Matching by Customer name is also not a good idea (not even in Access), as customer names are not unique, among several other potential issues that can keep name based relationships from working.
But with this relationship:
Table1::CustomerName = Table2::CustomerName
A given record in Table1 will match to all records in table2 with the same value in CustomerName--no matter what the date of the transaction. To get the count that you need, you either need a different relationship or a filtered portal.
Table1::CustomerName = Table2::CustomerName AND
Table1::TransactionDate > Table2::TransactionDate AND
Table1::cTransDate30 < Table2::TransactionDate
cTransDate30 would be a calculation field with a date result type defined as: TransactionDate + 30
To link multiple fields in one relationship and to use inequality operators in place of =, double click the relationship line to open the edit relationship dialog.