As indicated in the previous content reports for this anime, the seasons will be merged in a single one at a later date, not yet defined. The absence of dates on some seasons is a consequence of the current split and nothing can be done.

我觉得可以暂时引用每一季的第一集的播出时间，至于合并为一季的计划，目前也还没得到具体消息，所以完全可以暂时不考虑这个。 我提出这个问题的原因是因为我目前是按分季整理了资源，但是并没有每季的播出时间，所以不能根据播出时间排序来有序观看。

As indicated, as long as the merge has not been done, it is not technically possible to add a date to these seasons.