You can use episode groups for alternative episode numbering, e.g. https://www.themoviedb.org/tv/1429/episode_group/5fd0acbc798c940040c180b0/group/5fd0accee9c0dc003e376a71

The current numbering is correct. (https://en.wikipedia.org/wiki/List_of_Attack_on_Titan_episodes)

No, you wrong!!

read the rules for anime shows!

Anime Original Order

The main guidelines for animes are the same as with any other type of series. Our goal is to replicate how the TV series were originally released on their original network. The episodes of anime series should be in the exact order in which they were originally released in Japan.

In most cases, the original airing order (how it was first released) will correspond to the order used by the official Japanese website (how it was supposed to be shown). However, we strongly recommend double-checking the original air dates and order with a trustworthy source.

The order used by the official Japanese website is sometimes different from the order the episode were originally released in. This usually happens when the episodes are first aired out of order on TV, when episodes are banned from airing after the initial Japanese TV broadcast or when regular season episodes are first released with a DVD release. An infamous example is the 38th episode of Pokémon which triggered seizures and was banned after its initial Japanese TV airing.

Furthermore, international releases of anime series often have episode orders, episode counts and season splits that are wildly different from the original Japanese release. International broadcast should not be used as templates for anime.

....

Should I add new episodes to the existing season, to a new season, or as a new series?

The answer lies with the original Japanese data.

Long-running series with continuous episode numbers (e.g. 867, 868, 869) are added as a single season.

Sequels series (i.e. a direct continuation of the story) are added within the same entry. When the episodes numbers are continuous, all episodes are added to the same season. When the episode count is restarted (i.e. the first episode is Episode 1), the new episodes are added as a new season.

Episodes airing in a split cour format (e.g. Episodes 1-13, break, Episodes 14-26) are added in a single season. Examples: AKB0048

When a series is released in two or more parts, the new episodes should also be added to the same season when the episode number are continuous. Sometimes the production of new episodes is halted for a year or more. Examples: Fairy Tail / Fairy Tail (2014), Dragon Ball Z Kai / Dragon Ball Z Kai: The Final Chapters, Naruto / Naruto Shippuden

On the other hand, reboot series, spin-off series, series set in an alternative timeline, new adaptations based on the same source material, ... are added as a new TV entry. Examples: Digimon

We strongly recommend using the official Japanese website. Databases such as anidb, MyAnimeList and Anime News Network, or trustworthy sources such as Syoboi can help you make informed decision, but they should be used with caution. And please keep in mind that every database has their own, unique guidelines.

The officeial side of the show use absolute numbers - Attack on Titan Episode 76 and in this case should only all episode in one season. Seasons are irrelevant and should design in a group with type production.