Since the mounting hardware you already have from your previous TV does follow VESA, you would be returning the new one for that reason.
Unless, you know, it was amazing, like completely dumb with no registration step, and offering great picture quality. That might be worth drilling some new holes in the mounting plate, or whatever it takes to make it work.
When I say returning, of course I mean not buying in the first place! "Does it have a standard bolt pattern compatible with my intended mount" is one of the first things you check for in the technical specs, long before you order something or go pick it up. If your mount is strictly 100x100, you can't have a larger TV on it that has a 200x100 or 200x200.
Unless, you know, it was amazing, like completely dumb with no registration step, and offering great picture quality. That might be worth drilling some new holes in the mounting plate, or whatever it takes to make it work.