I read somewhere recently that chokes were introduced around 1870 so there is a gap of 5 years where this was not indicated by proof house stampings. I would suggest it would be prudent to check any early breach loaders which are not marked not for ball or choke as they might fall into this time frame and it would be a shame to blow the end off one of these venerable pieces.
The question is actually regarding percussion shotguns. I see there has been recent discussion on this forum over muzzle loading and chokes. http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=224471#Post224471
I dont think you need to worry too much about muzzle loaders if you can push it down the muzzle it will likely come out the same way.