Here is another, more detailed "tutorial" to try and explain the difference between pure BD and BD/Leo stingrays.
Typically BD rays are distinguished by more spots, by bigger spots, and by more irregular patters; in time the bigger spots often lead to "doughnuts" where there is a black hole in the middle. Then the black in the middle typically creeps out, producing a "C" white shape, as opposed to a "doughnut". This is called eclipsing. A normal BD/Leo and certainly a normal Leo will not experience this. Here is a video showing typical BD/Leos:
I have also attached a couple photos of an adult pair of BD/Leos that I raised and later sold.
Now compare the video above with a video of the pure BD pups I raised last year (also kept for over 12 months). You should notice quite a difference in the number of white spots, the size of the white spots, and the presence of doughnuts and eclipses:
BD's are also known to have belly spotting. You typically will not find much belly spotting on a BD/Leo, and none at all on a Leo. You can see a good example of belly spotting here:
Pure BD's typically also get spontaneous spots that just appear randomly anywhere on the ray's disc. These spots can grow in size and in time go through the doughnut and eclipsing phase. BD/Leos and pure Leos rarely have these spontaneous spots, or if they do, not as many nor do they grow as large.
Finally, both BD/Leos and Leos have white spots around the outside edge of their disc. As the ray grows, these outside spots "move" inward and enlarge in size. The more spots on the outside edge, the more spots your ray will have in future. BD rays typically have far more spots around their outside disc and these spots typically grow larger and more dynamic.
In conclusion, pure BD rays typically have more spots and larger spots that undergo more change (doughnuts and eclipses) than a BD/Leo or Leo. Compared when young, pure BD's and BD/Leos may look similar, but when seen as adults, there is no comparison; a pure BD adult ray is more striking in appearance.