More or less, I have the follows on everything I took an interest in and am still building it up
Some things like the group removing everything and creating a void is annoying, its also, at least for me, annoying to see a new chapter only to realize that the chapter is something I have already read.
so for a flag, sub new, as in the current chapter is 50 but they released lets say a remake of 23, it would be tagged as sub new.
In the case of a volume extra, unless the manga is being translated WAY later then current release, you wont get volume extras, but a chapter 50 current with a 23.5 would also be released as sub new, while it would be a new chapter, and it would still be sub new, given how many things end off on cliffhangers seeing a chapter i'm waiting for and that its new come out only for it to be an extra...
Now, you bring up a potential naming difference, this is also something that I don't see happen all to often and would be an edge case,
i'm not sure how many people there are like me, but i'm at 289 manga and increasing for my reading list that I keep up with, the actual number is probably nearing 1000 when I take into account off site manga and things not in it yet, and when I read a japanese name, I just shrug my shoulders and I have no idea what it is before I go into it, there are probably 50 manga I know off the top of my head that aren't english names, but the rest are honestly going in blind till I see art or characters most of the time, even with english names, some of them blend in with each other so much that its hard to tell. A sub new tag would at the very least for me stop getting my hopes up when I see a new chapter was released. I just think the heads up that something isn't where it's currently at would be nice, given a few groups are going back and retranslateing things that got pulled.