I am aware of at least two versions of the tender on this model being delivered over three production runs.
The first two runs did not have any contacts installed on the tender trucks. Curiously, the models I used for this How To had all of the provisions in place to install them! They simply lacked the parts.
The third run had axle wiper type pickups and was an improvement over the earlier models but this design is not very effective as there is limited sureface area at the point of contact and very little pressure applied to the joint.
SBS4DCC.com offers products to improve the performance of either version.