Column in INSERT query needs to increment if matching data on rows is different
This is where views come in handy, and an understanding of relational databases. You can store each entry in a table dedicated for that. Each entry can have its own PK value that lets you differentiate between it. However, each entry can refer to a separate table to identify the Customer, Order, LineSeq. If you need to insert an entry for a Cus+Ord+LS that doesn’t exist yet, you create a new one, with its own PK value. Then you create a view which joins those two tables, including a COUNT_BIG(*) aggregate to count how many times they’re used. You could even index the view so that the values are worked out ahead of time.

To use this the way you want, you could put an “instead of trigger” on your view that handles the inserts/deletes into your entries table. That’s essentially a procedure that you interact with by doing inserts into a view, even though your view can’t handle inserts.