Well... Remember the airing pattern Sesame Street follows for it's newer seasons. They take the total of twenty-six episodes and divide them into a first run of the first fifteen episodes, and then there's a second run of the last eleven episodes. The first week of the season's premiere, they air the first five episodes of the new season. The week following that, they begin an on-and-off mix of rerun and new episodes. It works in one of two ways.
Model A:
Week 1: Season premiere, all new episodes.
Week 2: Monday, Wednesday and Friday: New current season episodes; Tuesday and Thursday, repeat episodes from past seasons, usually two seasons previous.
Example: We're at Season 38 now, so the repeats are from Season 36.
Week 3: Monday, Wednesday and Friday: Repeat episodes; Tuesday and Thursday, new current episodes.
Model B:
Week 1: Season premiere, all new episodes.
Weeks 2 and 3 are an inverted form of Model A's second and third weeks.
This goes on until the first fifteen episodes of the current season air, about up to some point in September. Then repeats of the previous and current season air until mid-November when the last eleven episodes of the season air.
Hope this helps explain things.