Yep...but--
Cleverly worded, but you're missing the point. Regardless of mfr, all "standard" size toilet bowls are the same dimensions and all "highboy" bowls are the same dimensions. So unless you're measuring to see whether there's room for the larger bowl, if the base of the new toilet is to sit in the same place as the old toilet, measuring either half of the bowl will tell you whether the other half will fit. So once you position the base, if the front half of the new toilet doesn't extend any further foward than existing bowl does, the rear half won't extend any further back. If the base has to sit further back, the back end of the toilet will extend the same amount as the difference between how far the old bowl and the new bowl extend forward.