This is one of the weaknesses of English. Languages that have explicit progressive tenses or subjunctive moods are much clearer in indicating things like this.
That said, I think that interpreting the tag definition as "Must include sex scene with 3 or more LIs" is probably incorrect here, because that would be much closer to an orgy, where a harem (to me) implies an ongoing relationship. If I was going to be That Guy, I'd say that grammatically it is more an insistence that all participants in a harem are having sex with everyone else, but that's also not how most people interpret the tag.
Regardless, I think focusing on the "letter of the law" as it were is futile to some extent. Words mean what people use them to mean, regardless of dictionary definitions. Prescriptivism is dumb and wrong.
[/soapbox]
I'll start off by saying that I do
not agree with the tag definition of 'harem'.
However, to me, the definition is quite clear. I'll show it here again:
- Harem [1 person being courted by at least 3 others, all engaging in consensual sex simultaneously.]
As we can see there are two parts to their definition: the first that there must be at least 3 people; the second that sex between
all of them must be
simultaneous.
Here is the Meriam-Webster definition of 'simultaneous':
1 : existing or occurring at the same time : exactly coincident
To me that is absolutely clear as to the meaning, especially those last two words. It's difficult to interpret it as something else.
Perhaps the rule makers at F95 do not understand the English language very well. Nevertheless what is written is quite clear.
I understand that word definitions may change over time, but not overnight.
You might disregard dictionary definitions, but there must be some agreement as to meanings or all communication will be impossible. You can have your own interpretations, but unless the people with whom you are communicating have the same interpretations, they will not understand what you said. For instance, it is obvious to me that different people here on this thread have different interpretations of what a harem is.
So I will repeat what I have said before: the tag rule (imperfect and perhaps incorrect [insert your own modifier here] as it may be)
is what it is.