It's a best guess calculation (statistics) based on some "known" info. Here's something based on colors and models for Challenger Example: 955 R/T convertibles built Plum crazy was most popular color at 22.2% So best guess is there were 955 x 22.2% = 222 Plum Crazy R/T convertibles built that year.
Those are one line item row numbers from Chrysler.
I believe the OP is referring to combining multiple row of options. There are other individual option reports that chart an option per body and/or model type. Then mis-using statistics with bad reasoning.