If the goal is to match IMDb, since it's the only complete source then you should know that the first issue is in Season 5 where IMDb has it ending with "episode 20" and TMDB has it ending with "episode 15" - That is using IMDb as the guidebook on episodes which is a debatable idea since....

Issues using IMDb as the guidebook are apparent in the current season. IMDb is not aligned with what WGBH says are episodes for the current season AND IMDb has episode airdates and numbers that WGBH doesn't mention at all.

Wikipedia has no data for the current season except episode 1

TVMaze shows seasons by year. They are aligning with what WGBH is listing on their website.

According to IMDb we are not in season 42! We are in season 41... many of the torrents for Frontline are aligned with that idea as well although their episode numbers differ.

Without an accurate and reliable source then I am not sure how we align the episodes on TMDB.

I have sent a request to WGBH production team requesting an accurate list... maybe just maybe they will assign an intern to email that out.