the 60th Congress of the United States, Copyright Act of 1909 — Pub.L. 60−349…
“ That where the copyright proprietor has sought to comply with the provisions of this Act with respect to notice, the omission by accident or mistake of the prescribed notice from a particular copy or copies shall not invalidate the copyright or prevent recovery for infringement against any person who, after actual notice of the copyright, begins an undertaking to infringe it, but shall prevent the recovery of damages against an innocent infringer, who has been misled by the omission of the notice ”
