I also have a table manufactured by the Extensole Corporation. They were based out of Sparta, Michigan. The table I have has a patent number and trademark number printed inside as well as a three digit number which I assume is the production number. The trademark number I have on my table was registered in 1938. The trademark number is 2,153,262. If you find a number on yours that is different than mine, then go to www.uspto.gov
and you can research it. I'd like more info on the Extensole Corporation also if anyone has any. My grandmother refers to the table as a harvest table but any pictures I've seen on the internet of harvest tables look much different.