Hello,
I just went through a battery of tests with collection letters and I have found some questions.
A) Not sure if this stamp is new (i think so) not sure what it brings to the table?? Why have 2 fields with the same information? Not useful and confusing to the customer.
B) Why there is no option to exclude customers from the collection letters? There should be a check box just as the one for excluding fees and interest directly on the master. Now we need to figure out a super manual workaround. Using different posting profiles or filtering the batch, or cancelling the created letters is not a smart way. What is the logic to make this so complicated?
C) I'm not sure the reason, but the system creates 2 letters, the same code (Letter 3), for the same customer. 2 possible reasons a) sales order invoices are separated from FTI invoice or b) Billing classification used (but in the setup of the billing i say to use the collection sequence from the posting profil) Non of the 2 reasons are acceptable.
It clearly separates the invoices 
There should not be the same sequence code for the same customer.
3) Last question is how can i generate a manual process? Lets say the final letter, I create a separate sequence for the letter # 4. And i want to send it only a some customers? I did not see where i can chose the combination i want to generate and send.