Hi Bob! You are very welcomed here
. I agree. Yes, around these parts that it is also what it means, a second version of a previous model and as you say normally the hull remains even if the keel, ruder and sometimes the transom are modified.
Today most brands prefer not to use that denomination anymore and just pretend that a MKII is a completely new boat.
That's better for marketing: Most will prefer to have a completely new boat than a second version of a previous model even if sometimes the hull is still quite modern and up to date in what regards performance.
sometimes with the same hull some brands manage to produce quite different looking boats, in the interior and on the outside look. That is the case for instance regarding the Salona 38 that could be called 37 MKII instead.
I talked with them when they were designing the 38 to know if they were using the same hull or not and after what seemed to me an hesitation they opted for the same hull and asked Ker to design a new keel and ruder. The reason was that the 37 was still winning races at top level (and is still a very competitive boat) so they decided to modernize the look of the boat, give it a better interior, work on the appendices rather than having a new design that could perform not so well.
But as most that buy their boats are not racers and don't know that the 37 is still a very fast boat, if they called it 37MK II, they would not seel it so well, so....the "new" Salona 38 appeared on the market