I think that one of the problems is that the term aren't all well defined.
For example, in biologic taxonomy, you have Koala Bears, Panda Bears, Polar Bears and Grizzly Bears. Are they all Bears. Not quite. Koala Bears are marsupials. Panda Bears are more closely related to red pandas, raccoons, otters and skunks than true (Ursa) bears.
In the same way, the taxonomy of LGBTQ+ is also unclear in many areas.
The difference between Bisexual and Pansexual (IMHO): Bisexuals (bi meaning 2) are attracted to (only) (manly) men or (feminine) women. Pansexuals (pan meaning all) are attracted to the entire spectrum of men and women and anything in between. I know a GG who classifies herself as pansexual and married a MtF transexual.
Another anomaly. What is the definition of bisexual? Think about a GG married to a man who had a romantic GF in college. If you've only had one same sex romantic relationship, are you forever Bi? How many opposite sex romantic relationships do you need to become hetero (again)?
I think this thread does more to divide us than unify us, and I think that we should be unified on the spectrum.