In light of Lewis' rocket ship wearing a F1 skin suit, I hypothesize that Mercedes were willing to sacrifice Bottas as far back as the Italian GP which was 5 races ago. Further, his subsequent ICE replacements were for R&D purposes more than typical wear and tear on a normal timeline. These PU's we're tuned for short life/extra pace and Mercedes needed evidence of longevity.
At Monza Bottas got his new PU, and was a*** to beat Lewis by nearly a tenth of a second in quali. He proceeded to win the Sprint race and then snatch 3rd after starting 19th in a very impressive drive. Undoubtedly, Max and Lewis playing dog pile on the beach made that podium a reality, but no less, he climbed the grid.
Bottas go another PU in Russia, and there isn't a lot to say here because it wasn't the best drive he has ever had, but far from the worst.
In Turkey, Bottas had a phenomenal Grand Prix, getting his first win. For a guy who historically stinks in wet/damp conditions, he certainly made it count. Call it clarity about his future, I call it confidence in the car performing and less worry about pushing to the aero/grip limits in turns.
At the US Grand Prix, Bottas was once again fitted for a new ICE, one he is still running. This race was not his best display.
3 weeks later Lewis gets his new ICE and the rest is history. Mercedes spent 2 months testing Bottas engine wear dating back to September 12th. Now with this data they are ready to make the final run in over the last 3 grand prix with a sneaky strategy that may see them give Lewis one more ICE before the season comes to an end.