I have too, but that was with prefab cork. Im sure its easier to turn handles without a reel seat on there. Blank butt right in the lathe chuck.
I glue my seat and cork rings on the blank all at once..that way, everything stays where it should be, with nothing shifting out of position. I guess nothing wrong with separately, but why would they?
Just a word of caution, on three and four piece rods sometimes the welt on the female ferrule is larger than the diameter of the shaft under the grip, don't ask me how I figured that outI reshape my premade cork grips with my elec drill chucked in my bench vise. And since the butt section of most bamboo rods are a lot bigger in diameter due to the taper, I put the cork grip on the blank over the ferrule, reelseat last.