It doesn't make sense to amortize model training over multiple years since they train multiple models per year (e.g. Claude 3.5, 3.7, and 4 were released within 12 months). Or you can, but then you have to overlap amortization schedules multiple times over. E.g. if they amortized over 24 months, then they would still be amortizing Claude 2.1, 3, 3.5, 3.7, 4, and 4.1.