Is it possible to achieve a 100% transported percentage?

According to an entry related to industry transportation percentage:

Industries may decide to keep back part of the production and not deliver it to any station.

...which may account for the lack of perfection. (Not that 93% is worth complaining about, mind you.)

On a related note (based on the answers to this question) it would seem goods that are still in transport aren't considered delivered and thus are not counted towards the transportation percentage. Since the percentage is calculated for a month, that may account for the difference (when the end of the month arrives and there are still goods on the track.)

The calculation mechanics can be found here, as well as a (currently nonoperational) link to the actual code making the calculation.