Gary:
Assembly lines are specific to the plant they are located in. Lines 6, 8, 32, 16, etc are in one plant. Lines 1, 2, 3, 4, etc are in another plant. there are no duplicate assembly line numbers. If a line is shut down or replaced the original number is "retired" and a new one is assigned to the replacement line. If a new product assembly line is installed, it gets the next number on the list.
If the same filter PN was run in different plants at the same time, they would still have different lot numbers due to this.