Here is where the British may have gotten something right.  They don’t even use “gotten” anymore except in a few British sayings that no decent American would ever use anyway.  After all, there’s no one in our country who would dare profit from ill-gotten gains!

Generally, or at least in theory, “gotten” implies the process of getting something, and “got” is the condition of having gotten that something.  For instance:  “I’ve gotten out of jail... what... six times?  But now that I got a gun, I ain’t goin’ back.”

However, if you said the same thing backwards it really means the same thing:  “I got out of jail, but now that I’ve gotten a gun... yeah, you know the shtick.”  For that matter, any combination would be pretty much the same.

And if that’s not confusing enough, “gotten” is not always the past participle of “to get.”  When you are using “to get” to mean “must,” then “got” becomes the past participle, as in: “That dress has got to go!” 

Some would argue... those who argue over such things... that you also don’t use the past participle with the helping verb when you are wanting to say “has” or “have,” such as, “She has got one hot waffle iron.”  Of course, that’s just plain silly.  First of all, it’s not that hot.  And second of all, it’s just bad English.  Why would you need “got” at all?  It’s a bit like saying, “She has has one hot skillet.”

I suppose one could argue, if you really need something to argue about, that we truly don’t need the verb “to get” at all, including all of its evil-spawn conjugations.  After all, we’ve already gotten “become” and “acquired,” and if you’ve really got to say “must,” then say “must.”  Or, you can do like I do:  Ignore it.