I think a console lifespan of eight years (so 4 years each in first and second half) would be more accurate. Consoles that are relevant to the market for ten years are exceptions rather than typical. That said, great data and I loved reading the analysis on it. Thanks!
I agree that 10 years is a lot for most consoles, especially if you consider good selling years, my idea is not try and split sales in two halves, but rather to have the strong first years compared to the end, what you could consider having good legs.
Most consoles peak between year 4 and 5, so I understand why you would want to compare the first 4 years. I did the change and it seems like it is very interesting, specially because you see how X360 and PS3 sold more after year 4.
Good idea, it might be better to view it this way. There is no real correct way to analyze it, so seeing things from different perspectives is always fun.