We wish to find all payments (applications) in A/R that were applied for a single customer check.  We found a number of applications for the check in our RM30201 table (that's not unusual).  But we found some of exact same rows in our RM20201 table (this is what was unexpected.)  If we total the rows in RM30201 we see the total of the check is applied, for example, to 30 invoice documents.   But about 10 of those rows are also in RM20201 at the very same time

We need to understand why this is the case.  Any ideas, pointers, knowledge transfer available will be greatly appreciated!  A humble thank you in advance.