Terry, I am the novice here. I started with three tiny cuttings, purchased from a grower in Maui over 25 years ago. Back in those days, and I am guessing here (Hetty will know), there probably were not many hybrids available. Now there are probably 1000's! My three were the Celadine, Scott Pratt, and Vera Cruz Rose. The Scott Pratt was the very first plumeria to be recognized by the PSA and the Celadine is considered by many to be the Queen of the Plumeria world. She's been around forever. Again I am guessing here, but perhaps those older varieties are more resistant to all the stuff mentioned that either weaken the plants or kill them outright.
I showed you the actual three "Mother" plants. Here are their flowers:
drdawg (Dr. Kenneth Ramsey)
The reason it's so hard to lose weight when you get up in age is because your body and your fat have become good friends.