I think that points scored by the leading team in “garbage time” are the ones that should be discounted, not the trailing teams’. There has been research done that shows that being able to score points while trailing in “garbage time” is something that is indicative of being able to score points in other situations. On the other hand trailing teams will take riskier options leading to more turnovers, leading to more point scoring opportunities from playing on shortened fields. Sustaining long drives in and of itself creates more turnover opportunities, as each play run has a roughly 1% of being a turnover. If your plan is to put together series of long dozen+ play drives, then you are going to give your opponent more opportunities to score TDs.