" the general consensus it seems is to not show anything that hasn’t made it into the market"
If this was completely true there would be a lot of designers out there with empty portfolios.
If you are going to a competitor, there will be issues. If you are interviewing with your current boss’ best buddy and they chat over beers, there will be issues. Otherwise I think leaving no documentation and being reasonably aware of any trademark/IP issues that could cause problems will be OK. Its been my experience that consulting firms even do this - not showing Coke what Pepsi was working on, of course, but it might be OK to show Brooks Shoes or a real estate company what Pepsi was working on.