I think there’s a few things to consider
Remember that the models aren’t created by historians, but by 3d modellers. Which are only doing their job. They are often using pictures, or if lucky, 3d scans, of museum pieces if available. Though obviously sometimes the modeller is given reference materials from several vehicles and thus creates a hodgepodge model. Though I would assume the latter is more often true of vehicles that have few and hard to access examples, or no surviving examples at all. In which case they make do with what they got.
Since there are many surviving IS-3’s in museums it seems likely one was used as reference as opposed to several, but it’s also hard to track down which one was used as reference.
To add. The model isn’t based on 1945 production since none survived in their original 1945 configuration, and getting reference material for it is harder. Hence it’ll obviously be one that saw some modernisations before becoming a museum piece.
And of course minor differences between vehicles are present always, as basically no military cares to standardise each vehicle down to the bolts. If several workshops works on the modernisation, and one has access to different headlights than the other, no one cares. Especially when modernisations span years and parts become unavailable, or improved, but not so massively improved that it’s worth going back to the vehicles that have already been modernised. Or during training one is driven into a tree and smashes that headlight, and is given whatever headlight is available that fits the same spec.
It could at least be modelled after the IS-3 at The Museum of Russian Military History in Padikovo. As it seems to generally match the same characteristics, at least frontally. The only mismatch I can find on it is the length between the log fasteners. But I also don’t know enough about all the changes done to IS-3’s to know what to look for.
