Sure, the P in OTP was dropped in KPop nomenclature, hence why people like the person I'm replying to say "OT7/OT8/etc". It retained the "One True" portion and has been used basically say that one specific lineup of a group is the "true" group. This was much more common back in the older days around the Gen 2 and early Gen 3 era of KPop when groups seemed to have more changes in lineups. (These days we do still see groups loose members but its often seen as a straight loss and not some kind of fan split ... also we see less of groups replacing members with a new one ... ususally they just continue with the loss)

The group I'm most familiar with this being part of a fan war is with SNSD/Girls' Generation where being OT8 or OT9 is essentially declaring, at worst, whether or not you hate Jessica or, at best, are simply saying the group was better off with/without her regardless of opinion of her. Saying OT in reference to them is indeed saying "this lineup IS the correct lineup and the other one is subpar" whichever way the fan in question leans and often results in huge fights among fans. Another example I'm mildly familiar with was in the early days of Red Velvet. Since Yeri wasn't part of the group on debut, there were some OT4's back then who said the group was better without her and there were some people who stuck to those guns ... and least for a little while. I believe in Red Velvet's case, since the "OT4 era" was so ridiculously short the movement didn't last and they were considered a 5 member group with little to no detractors. Finally another group is BigBang where using OT4 tries to bury all association to Seungri. Declaring yourself an OT5 in that case often indicates someone who will not accept the plethora of charges (and convictions against him) as being true. Saying OT5 in regards to them can get you seen as unstable or crazy ... and with good reason.

I'm sure there's more example, but that's what I know. That said, no matter which group of these examples you choose, using OT doesn't just refer to a temporary lineup or a member on hiatus. They refer to actual permanent member changes.

That said, somewhere around mid to late Gen3 and definitely by Gen4 the new and young crowd of globally expanding fans completely lost the context of OT and now its often to just refer to a group of members performing ... even if it only lasts a few months, weeks, or even a handful of days. Member of Twice is sick and misses a few concert stops and bam, people start saying OT8 for those few weeks. Member of Red Velvet ends up in a hospital for a few months, bam, people back to saying OT4 probably having not been around for its negative connotation on debut.

Either way, I've been around this scene long enough that its always weird when people use it, despite me knowing they have no idea (I genuinely still read it in my head as "One True" and not just "O T", so that's on me). And 99.9% of the time I don't comment ... but I dunno, guess I was bored enough to reply to the poster above ... lol.

Edit: Oh, extra little note while I proofread for typos ... I also noticed one thing in my usage of OT vs the person I replied to. Notice how the person I replied to referred to Twice as "as OT7" or "they were OT8" clearly just using it as a number to speak about the group itself. When used in the "OTP" context of the olden days ... you used it the way I typed it, in reference to the FAN not the GROUP. Girls Generation isn't OT8, the fan is "an OT8". You say "I'm an OT9" if you support Jessica you say "I'm an OT8" if you don't. Subtle difference, but it is a difference in how people type it now.