It doesn't work this way.

If Alphabet wanted to prove they lasted three years, they would have found a way to prove it. Auditors don't go around challenging on things like this. In particular, they don't go around challenging companies on depreciation because that is a key lever that management can pull if they need to hit numbers.

It is very difficult to discern exactly why they will have done this but the functional answer is: they have done this because they needed earnings to increase. In this case, it looks like the difference between a 15% and a 20% beat (I believe the change was made in January, I think they had quite a big beat in that quarter after some flattish momentum, middle of the year very strong anyway).