They can't really change the definition of voluntary or mandatory. Either you are in the club or you are not. The difference with mandatory is that the club rules are written in to the condo CC&Rs. The definition of voluntary is simply that you can opt out of the club and that they don't allow people who buy resale at those resorts that don't have the club rules written in to the CC&Rs to voluntarily join the club.
If they change the club rules, they impact all developer purchasers as well as those that own mandatory resale.
Not trying to start an argument here -- I researched this when I bought the 6 intervals in SVV. There is a club affiliation agreement that is referenced, but that can be changed at any time by the club operator. There was no mention of mandatory or voluntary at least in the SVV documents that I checked. I'll try to dig it up over the weekend, but it has been so long since I purchased, not sure where I stored them. I'm sure in the agreement, that there are specification of mandatory or voluntary, but the CC&Rs are very careful to reference the affiliation agreement and stress that the club operator can change the rules at any time.
I think where we disagree is that I believe the club rules are referenced, but they are not actually written into the CC&Rs themselves. That gives the club ability to change rules across all properties without having to re-record amendments and get board approval every single time there is a change.
Could this have changed? Yes, I didn't check every single amendment to the CC&Rs so possible but I doubt it (hence my 51% guess).
Yes, if they change club rules, they change it for everyone.
-ryan