Tesla do a bit of both, last year they updated the vin year in November whereas they used to do it on 1st Jan, and at that time they did the spec changes like frunk hooks going, boot liners, different coloured wheels for the M3P etc changing with the year letter in the vin. So I think for the model 3 they make running changes on anything that’s not a formal spec change and a yearly spec change. Eg a change to the under panel that got wet and disintegrated they’d do as soon as they can, but adding something like the heat pump will be a model year change,