I would think it not too unreasonable, that after one pass through w/o finding your assigned slip, you just tie up to the fuel dock or the end of the pier and sort it out in the morning.
After cruising around a marina one night (a rather large marina) and not finding the guest slip or the fuel dock, I then kayaked around for an hour until I finally gave up. I tied up to a derelict dock and headed out in the morning sans hot shower. It was not the most fun I've ever had. Would have been heaven to be able to find the slip, have a hot shower and use their bathroom. Often marinas will leave the key in the dock box for you so you can get through their security gates. But if you can't find the dock box you're punished with no shower and no electricity, etc. The joys of sailing!