We always follow the original release data, which you can find here:

• official site: http://www.haremking.tv/story/
  
• syoboi.jp: http://cal.syoboi.jp/tid/4857/time
  
• anibd.net: https://anidb.net/anime/12498
  

All these sources prove that there are actually 13 episodes in season 4. The other sites place "Holiness Behind the Gym" as a special or E00 just because the original name of this episode contains "life.00", but as for numbering this is actually 1st regular episode of the season, not a special. And because we always start numbering from E01, the episode "Holiness Behind the Gym" (life.00 『体育館裏のホーリー』) is S04E01 and the last episode "Lion Heart of the School Festival" (life.MAXIMUM VS power.MAXIMUM『学園祭のライオンハート』) is S04E13.

Sorry to bother you again.

There seems to be inconsistency on this website. There is another anime that has an episode that aired the week before, but is treated as a special. If all you were to go by were the date then My Hero Academia season 2 should contain 26 episodes.

Is the context of episodes not considered when determining if an episode is a special?

"Holiness Behind the Gym" does not have any direct continuation in life.01. It was an episode created to retcon some of the final episodes of the previous season due to liberties the first production company took. It could almost be considered a recap for the final events of the previous season. (With an extra scene at the end).

I believe a fair fix would be to change the website to allow an episode 00 to be added to the seasons with a connection to a special. Then you could accommodate either organization preference.

I am sure I am annoying you, but I do apologize for that.

There seems to be inconsistency on this website. There is another anime that has an episode that aired the week before, but is treated as a special.

What series/episode are we talking about?

Is the context of episodes not considered when determining if an episode is a special?

"Holiness Behind the Gym" does not have any direct continuation in life.01. It was an episode created to retcon some of the final episodes of the previous season due to liberties the first production company took. It could almost be considered a recap for the final events of the previous season. (With an extra scene at the end).

If it is recap episode, it should be added as special. I'm not familiar with this series and I'm not able to get it to check, so I'm leaving this thread open for another mod to reconsider. Until then, we will keep current episode order.

I believe a fair fix would be to change the website to allow an episode 00 to be added to the seasons with a connection to a special. Then you could accommodate either organization preference.

We don't allow E00 and I don't think this will ever change...

I am sure I am annoying you, but I do apologize for that.

No problem at all! If your request is legit, we will gladly change our data. However, we will have to wait and investigate for a while, as we can usually use the order presented on syoboi.jp and anidb.net (if it is the same), but if there is error on their sites, we indeed want to have it corrected.

As I see, the previous seasons (from 1 to 3) has only 12 episodes. So, according to this fact it may be reasonable to mark s04e01 as special, in order to season 4 will contains 12 episodes as in previous ones.

As @talestalker said, we always follow the official data. Most times TV special episodes are not part of the regular seasons, but in a few case like this one they are. If you're not happy with the official order, feel free to create an episode group with Holiness Behind the Gym in the specials.