OK here are some examples to offer to the discussion and illustrate what I found and mentioned in my last post. Production dates are approximation on most.
Choose to place the cars in order by when they were likely or actually completed mixing plants together this time
9R111615 -Built around 10/68
9R111073 -Built around 11/68
9R114465 -Built around first part of 11/68
9R12424 -Built around 12/68
9F481236 -Built 2/26/69
9F481888 -Built around the end of 3/69
9T02S19089x -Built around 4/69
9F482728 -Built around first of 6/69
9F483132 -Built around mid or late 6/69
As you can see these are all the S style/version across pretty much the whole production year
Hope this helps