What happened to Odie & Leslie Harrison around 1920?

Recently, I've been going through trying to clean up my tree & find the holes in my research.

This got me to my most recent brickwall- Where were my great-grandparents in the 1920's?

My great grandmother married my great grandfather in 1926.  I know this because I found them in the Muhlenberg county marriage record.  However, in my great grandfather's WWI draft register, he list himself as married?????? 
(I believe the marriage record is the actual date since my grandmother was born the 

following year.) 

U.S., World War I Draft Registration Cards, 1917-1918

Whether they were married in 1926 or around 1917, I still can't find either one of them in 1920.  

The only census I am sure that I have found my great grandfather, Leslie in is the 1900 census.

1900; Census Place: Russellville, Logan, Kentucky; Roll: 539; Page: 6B; Enumeration District: 0038

 The 1910 census list his parents, his brothers James (married to Adah), William, Richard & 2 other sisters-Queenie & Estella, (one of which could be the Eunice mentioned in 1900) but does not mention him.

 The only Leslie Harrison I was able to locate in 1920, that lived in Russellville, was married to a Katie.  

Could they be the same couple?

In 1920, she would have been 21 & he would have been 30-so the ages are close, but who is Katie? This made me question a couple of things:

1. Was my grandparents marriage their first marriage or was he married before?
2. Is this the same Leslie Harrison?  It is in the same county, near where his parents still lived, but that doesn't mean that it's him.  (Assuming that it is the same person is how my tree got so messed up to begin with.)

I guess my next step is to find out if there is another marriage record for my great grandfather or find out if there is more than one Leslie Harrison from Kentucky, who lived in Russellville, Kentucky.