You cannot copyright a licensed toy, model, or any other sort of artwork, at least in the US, that does not differ in some creative way from the original artwork that it is licensed from. Bachmann's Skarloey would fail this test, and so the only thing stopping Bachmann from releasing it as Talyllyn in the UK would be whether they own the moulds and such, which they probably do.
With regards to the accuracy of the TV series' CGI model of Skarloey, photographic references were indeed taken by the then-animators of the show, Nitrogen Studios. I doubt they made a 3d scan, as I imagine that would have been very expensive. The undersized buffers on the CGI model are from the two physical G scale models used before the CGI switchover. These models in turn got the undersized buffers from the Gauge 1 model used when Skarloey first appeared in the TV series. Thus the CGI model of Skarloey used currently is a combination of the fairly inaccurate physical models previously used on the show, and the real Talyllyn, which gives it such details as handrails and accurate sandbox lids. The Bachmann model on the other hand has none of these inaccuracies present on the CGI model. It is basically a model of Talyllyn with a face slapped on. The oversized cylinders on the Bachmann Skarloey seem to be an invention of Bachmann with no relation to any of the TV series models, physical or digital.