VT's only have two rays on a single branch whereas DeT's can have anywhere from 4-10 and sometimes more, HM's generally have 6+ although if they are nice enough they can have as little as 4 in each branch. For those who might not know what a ray is, take a look at this picture below:
Also known as Branching, I call the blue lines a Branch because then it branches out into the ray's much like a tree branches out to it's limbs/sticks. So we count the ray's at the end like this:
That boy is a 4 rayed HMPK. So VT's only ever have 2 ray's, if they have more than 2 rays it is a DeT or larger. Same with most CT's, they all have 2 ray's but we've bred them to be Double Double Rays (DDR, 4 rayed CT's) and even further for 6 rays and 8 although it starts to get a bit messy at that point.
Most PK's also only have 2 rays because they are the short tailed version of the VT's and then we start increasing for HMPK's. PK's are supposed to have more webbing though, that allows for a wider spread than most VT's can get even if they have the same amount of rays.
Back to VT's, there are a few different shapes the VT can take as I was saying previously. VT's can look sort of like a fabric or a cloth waving in the wind like this boy, that's more of the classic VT shape since it looks like a veil.
Then you get ones with more rounded edges like this one, this is more of the standard VT today though, of course depending on your area.
*Note this boy has a 180 degree spread but is not a Spade tail because he has no point, I'll get to that soon.
This lovely boy is leaning more towards the edge of a Round Tail and one more generation and I'd say they've got it!
Round tails are just rounded VT's, so they still only have 2 rays or are supposed to only have 2 rays just like VT's.
And young males will go through a "round" tail stage as they age. I think this is more along the lines of your question givemethatfish. And then as they age it will start to droop more and become the classic VT soon after ~2-3 months of age.
And Spade tail, it cannot be a Spade tail unless it has these two things; gets 180 degrees and the tail is very pointy as a spade is. As I said with the blue boy up towards the top, people may call that a Spade but it is not, he has the 180 degrees but lacking the point that they must have. This boy below is a Spade, even his point though should be a little pointier.
Here are two more spades:
This help everyone?