Correctly Identifying Plumeria
I feel the only way you can stick a tag on your plants with any assurance that you are correct is to buy from dependable sources that grow their own trees, or buy directly from those that buy and grow from those same trees. AND THEN, it is still important to observe the plants many physical characteristics, to make sure they line up with the cultivar's registration criteria. Many plumerias look similar in photos which has nothing to do with the reality of a full grown plant. Fragrance, flower size, leaf shape/size, hardiness, tree shape etc. are all established in a individual cultivar, and reliable growers work very hard to make sure the stock you receive is what has been set down. You just can't look at a photo and establish anything about a plumeria for SURE. By naming from a photo, or what looks similar to, you are potentially making what is already a very bad problem in plumeria worse.
Basically, if I have a plant I wanted to identify, I would put down when they bloom the color they are/fragrance and any other meaningful information, but NOT a name. That is reserved for plants that are collected from those who are concerned and careful about what plants they sell. The "unknowns" in my garden are some of my very favorites. It doesn't make them less a plant. It's just honesty. However, I think if you have been around these plants long enough, and a tag falls off a plant, and it blooms and it is a Guillot's Sunset or an Aztec Gold in every single way, you can be fairly assured that is what it is, but this is reserved for those that know their cultivars well and know what stock they have.
I have an AZ seedling that bloomed and guess what? You can't tell the difference between the parent and the seedling. This plant could NOT be passed on as an Aztec Gold in my book. Genetically, it just isn't so.
Some plumeria have established names and are specific plumeria sold by an established company. Not all established plants have been registered, but that is a whole new subject! Occasionally, some of the high volume companies sell "looks alot like" as the original, so again, know who you are buying from.
It's kinda like horse breeding...would you really want to buy a horse that looks like Man O' War, or a clone of him?
Edited from a post by Jean Thielmann (capini)