While Cal-Scale (Bowser) may well use their plastic parts to investment cast their brass AB brake parts, they still have the wrong dimensions.
Shrinkage during the casting process is 1.8%. If you multiply the prototype dimensions in the chart under discussion by 1.018, so as to predict the proper size of plastic piece that will produce the proper sized brass one, the numbers just don't work. The dimensions are just wrong. Unless there are errors in the table.
So any errors in the Cal-Scale parts are not based on making properly oversized parts for casting.