Copyright and public domain question?

I have an atlas that was published in 1921. As far as I can tell, it was not attributed to a particular author/editor/compiler, but to the company that is still in business and making modern maps and atlases. Because my print edition of the atlas was published before 1923, I ume it is public domain. Is that true, regardless of whether this company is still in business? And are there any restrictions on how I may use the maps from the atlas?