Prior to vacuuming a new cough, I vacuumed the rest of the house first (forgot to empty the bin assy). Would dirty contents in a vacuum, come out and spread onto the couch? My wife seems to think so. Says it's my fault the couch smells & is sticky.

You should direct this to dyson on their website or call the store. This asks questions of the community. Also a vacuum when working properly should never loose its contents back out the hose assuming that suction is not reversed, and that the contents actually was pulled into the canister.

If its a Dyson it shouldn't spread. Even if you didn't empty it. I vacuum my couch regularly in the middle of everything else.