Some strength of schedule models calculate strength of schedule based on the opponents the team has faced to date. My model calculates strength of schedule based on all the opponents on a team's schedule. The reason for this is because it reduces weekly fluctuations.
For example, when a team plays their Week 17 game, in the traditional model their strength of schedule would change by 31 games...their Week 17 opponent's 16 games plus the additional game played by each of their prior 15 opponents. In my model, when a team plays their Week 17 game their strength of schedule will only change by 15 games...one additional game for each of the opponents on their schedule.