I also don't find that guideline in RC, assuming it's a misinterpretation of the edit to reach a drain time treshold rule.
I would agree that standardizing it would be simplier than arguing with other mappers. Wording need adjustement tho.
First, I've never seen "Sped up ver." and doesn't look fine in my eyes either (old site shows only 4 results for it (exluding results which aren't using "sped")). "Speed up ver." is more standardly used. "Sped" may be better grammatically speaking, but "Speed up" is the one used all across the web (like "value of "Speed" as been increased up", not as a actual verb)
Now the difference between Nightcore and Speed up is an issue here. Nightcore genre itself isn't really defined. It's a young style to start with and not a music genre in itself because it's mostly a modification of an other song. A definition cannot be set in stone. Some people will say it's trance and dance music with 160-180bpm and high pitch, including sped up songs, also kinda including happy hardcore, and others will just say it's sped and pitched up music around 10%-30%. Currently, youtube seems to go with the flow and use the second (more popular and agreed on) (
Youtube auto nightcore channel). There is no RELIABLE source for a official definition and I think the popular opinion should be used instead of the "origins".
I feel like speed up should be more like "well bpm is so low I can't make a good map, so let me just speed this up in audacity real quick" kinda of stuff, like
https://osu.ppy.sh/beatmapsets/240256 speed up by 100% (it's actually taken from
https://youtu.be/3IJUXFXbros which is labeled as nightcore, but breaks what I said about speed above, in both bpm and %, so yeah... idk anymore), and that nightcore should be used for what can be agreed upon as
nightcore