What was the last year that Porter and Coates published books in Philadelphia?

1904 was the last year that Porter & Coates published in Philadelphia. My grandfather was a night watchman and janitor until that year which was 2 years before my father was born in 1906. Grandpa had a large supply of their books which were given to employees when the company closed. Many of these books are still in wood boxes and unopened since about 1920 as I recall my father's stories about my grandfather. Some family memebers suggest there my some 'new' books there worth thousands. We'll see when we visit the warehouse in Phila., somewhere along Delaware Avenue and this is planned for September 2012. If we find this to be true we will certainly update this post with what we find.