Hi Zedster,I would be tempted to look at your problem from a different perspective. It sounds like each order can have multiple deliveries. I would be inclined to have a child table for deliveries rather than split a single order up into 3 separate orders. If you still wish to have separate orders with suffixes I would generate the incremental number as a text field using vba.
I was initially looking at using a child table for deliveries (screenshots of this are above) but the problem I had with that was getting it to work with my inventory control code. The code uses the product code and quantity fields in the orders child table to reduce the stock so I am unsure of how to change it to use the child table for deliveries instead. Unless the two child tables could work hand in hand maybe I wouldn't need to change it, but I don't know if that would work.
I don't have a problem with splitting a single order into 3 separate orders with letter suffixes as that is currently our company process. I am still learning vba so unsure how to get the incremental number to work that gasman suggested. I do like the sound of the idea though.