What a generation is
A generation is a body shell with fixed exterior dimensions, produced for several years. Within a generation, a manufacturer changes engines, trim and electronics constantly, but the panels — the part a cover touches — stay the same.
That is why a 2021, 2022 and 2023 example of the same generation take one identical cover, and why searching by year alone can send you to the wrong pattern across a generation boundary.
Where facelifts complicate it
A mid-life facelift usually changes bumpers and lights by a few millimetres, which does not change the pattern. Occasionally it changes overall length or roofline enough that we treat it as a separate generation — where we do, both appear separately on the model page.
Trim exceptions
Rear wings, sports bars and wide-arch performance trims genuinely change the required pattern. Those exceptions are listed on the generation page rather than buried in a size chart, because getting them wrong is the most common cause of a cover that will not seat.