Practically every TT membership sold has some differences from every other TT membership. You need to know the details of the specific membership you are buying, and you need to ask TT member services questions about which parks are included, which are not, which restrictions can be overridden, which cannot.
You will need the name and member number of the person selling the membership to ask those questions.
Otherwise, you will almost certainly be surprised that somethings are not as you expected.
The membership we purchased has a 21 day stay limit, but four times a year, we can purchase an additional week for $29. We stayed 28 days at Las Vegas in November/ December when the wife needed some medical treatment.
Getting into some parks can be a concern. Actually, I think currently / this past winter - Valley Verde in Arizona was the hardest park to get into. It is pretty ovbious which are the parks and seasons where longer stays may be difficult to book not far before arrival.
Such as Palm Springs. Only part of the winter is it difficult to get into that park. But the sites are limited by palm trees at the end of the picnic table, along with trees at both side of the site at the edge of the road, and a narrow road.
We needed to get the folks on the other side of the road to move their tow truck before we could get our trailer into the spot, and leave room for the slides on both sides of the TT to open.
A friend with a 41 foot Class A DP, could not get it into a standard Palm Springs spot at all. Palm Springs gets very crowed on weekends when it is open.
All the pull-thrus were occupied with long-term seasonal renters.
Seasonals or Personal sites are the biggest issue in TT parks at this time in my opinion. They take choice sites, leaving those who travel to back to back sites (one pedestal with two 30 amp hookups, two water spigots, and two sewer connections).
You end up with 5 to 8 feet between the service side of your rig and your neighbor, and usually not room for both you and the neighbor on the other side to each have a picnic table.
We bought our used membership through a broker, and it was a good decision to use them because they helped us ask several questions of TT member services, and we turned down the first two cheaper contracts to a slightly more expensive one with the parks we wanted to visit included.
Most common item is that the east coast Outdoor World or Mid-America parks are not included in most contracts which originated before the past 10 years.
Another item is that most of the resale contracts will not allow you to will the membership to your children, or to freeze your dues at age 62. Those provisions only apply to the original contract holder.
TT is currently offering to upgrade some memberships to Odyssey Unlimited - which is 28 day stays, 180 day booking window, includes 21 Encore Resorts which can be used under the same rules/ costs as TT parks, and a bit more. They told me that my membership could be upgraded to $6,800 and they would take payments.