I have seen this same problem, and see Quickbooks support doesn't understand the problem.

You should be able to have over 10,000 customers in your database, and QB should go thru all those customers without getting an error message of their being more than 4500 customers selected for statements. The program should first automatically filter the number of customers down to the number of customers that will actually need statements created automatically without the need to filter the customer list to 4500 first, and then generate the statements on that list of customers, which would then help out multiple QB users with this problem. Sure, there could be a limit of 4500 statements maybe to send out, but that shouldn't be a limit of 4500 customers selected initially, the limit should be based on the number of customers that actually has statements to be sent. That's how a good program would work.