I feel the absolute need to point out that even if "Group A" translates "Chapter #" it does not mean that "Group X, Y, or Z" CANNOT translate the same chapter (for better or worse). Particularly when "Group A" disallows uploads beyond their own designated sites (such as an Ad supported group owned website, or a Patreon paywall), or if they didn't do a decent job at it.
In fact, I would otherwise ENCOURAGE other groups to translate these chapters and upload to Mangadex. If not simply to do a better job, then in spite of the restrictions of the other group.
If "Group A" complains about "similarities" between translations (and "Group X, Y, or Z" didn't explicitly rip off the translation) then simply replying that they got the same result in translating from Japanese to English would suffice. If "Group A" persists that (other group) didn't have a right (for any reason) to do the translation or other work on the same chapter, simply responding either: "Legally, neither did you (or prove you have permission from the publisher/Mangaka)" or "Then sue us, meet us in court and explain why you have the right to translate this in the first place." would suffice.
tldr: I don't see why other groups are afraid to translate chapters just because they have been done before, especially if that translation isn't on Mangadex (or other similarly accepted websites). ESPECIALLY when some groups are still translating chapters when the entire series is licensed in their language...