OK--I'll be the one to display my ignorance and ask, "What are preverbs?" 
That's a new term to me and I don't find it in any of the standard Koine 
grammars I have here at the house. Since two linguists (Palmer & Olsen) 
and one classical scholar (Conrad)  recognized it, I'd assume it is either a 
specialized term from linguistics that I haven't encountered or something 
out of classical discussion. My hope is that I know what it is by a 
different name! :)  Mind enlightening me (and the others who are 
also wondering but not asking!)?

Rod Decker
Calvary Theological Seminary
Kansas City