Why are these manga labeled this way?

[Shelly]

So I saw this long list of related manga, but I sincerely doubt they are all in one shared universe.

Related:
Blade of the Phantom Master (Shared universe)
Burning Hell (Shared universe)
Distant Sky (Shared universe)
Island Part 2. (Shared universe)
Kangtawoo (Shared universe)
Neolith Girl (Shared universe)
Revival Man (Shared universe)
Terror Man (Shared universe)
Westwood Vibrato (Shared universe)

When I went to the comments (for https://mangadex.org/title/34344/housekeeper/comments/) I saw this:

KuroInfinity
Wait... did someone mess with the page? How are all of these series part of a shared universe? They don't even share the same authors...

RonBWL:
@KuroInfinity Unbelievable as it may sounds, the "shared universe" is correct, but in this case it's simply because all series are owned by one company and thus they're from the same "universe"

KraZTaco
@RonBWL So it's not that all of stories take place in the same continuity? I've only read Revival Man, but these two stories being in the same universe made no sense to me.

RonBWL
@KraZTaco They may, they may not, we'll never know. What we know is that, since they're from the same publisher, they're considered "shared universe" :v

I have never heard of it being done this way before. I want to know if this is an actual thing, and why? How did it start? For what reason?
If anyone has any information helpful to answering these questions, or anything that could give more context for it, please reply.

 

[AAA1]

@Shelly i don't know what those manga about. What i know is pokemon have many version of plot of story depending on the authors. It's a manga version. The old one have so many jokes (it's so hard to find it on internet) and the later have a complex story. The authors got same family name. I wonder if they are relatives. They are still in the same universe and not a doujin one

 

[Shelly]

@AAA1 @AbyssalMonkey
Alright. I now understand that there are probably some crossover between these series.

But I'm still confused about the reason that was given twice in the discussion/comments of Housekeeper manga:

"since they are from the same publisher/company, they are considered to be 'shared universe'."

Will this apply to manga that do not have crossover too? Is it a mangadex rule?

 

[AAA1]

@Shelly don't know. It could be a mistake. As one doesn't know until there is a clue in the chapter or officially announced by the publisher or author

 

[Holo]

You can always report these if you think there is an error.

 

[Holo]

I'll have to refer the question to @lymus, so I don't know enough about the series to make an informed decision here.

 

[juan_won]

I'm pretty sure you are missing one title out. It's called terror vs revival (or something like that) and it's new. It's a crossover between revival man and terror man.

 

[juan_won]

oh and idk if I should be asking you guys but for some reason when I go on terror man or revival man or any of them from the same universe, it doesn't show the other stories from the same universe. did I press something wrong my accident or is this a new update or something?

 

[juan_won]

😁