FWIW, the last column of the table is only used for locomotives classified as "Odd." The DSP&P Masons are classified with the first letter of "D" for the 2-6-6Ts and E for the 2-8-6s. The "D" is for moguls, and the E for consolidations, which would indicate that the system did not consider the tender truck on the Mason Bogies in the wheel count. The only DSP&P Mason Bogie classified as "Odd" was no. 5 (renumbered to 291), which was listed as a Mogul (not "13 wheel"). Based on this, I think it's likely that the note indicates six drivers or four drivers and a two-wheel pilot truck. Considering that the South Park added a pilot truck to their Mason Bogies that started out as 0-6-6T to make them 2-6-6T, it's a good chance that this was a 2-4-4T at the time of the UP renumbering in 1885.