The proper way to measure a rough-in is from the center of the flange to the wall behind the toilet. The standard is 12". to accommodate things a little better, some toilets are also made in 10 and 14" rough-ins. The rough-in has nothing to do with the length of the toilet, only the distance behind the flange to the wall.
So, even if the spec sheet doesn't show the distance to the front from the mounting bolts, it's fairly easy. Take the overall length of the toilet, subtract the rough-in and add back in the space behind the toilet. If your rough-in isn't exactly 10, 12, or 14", then you'd have to adjust for that as well.
Really, it just easier to measure your rough-in, and then compare the total length plus the designed in space behind to the wall.