Simplify the following text for a Grade 8 native English-speaking person.
Original: Eleven Johnson 78s were released on the Vocalion label during his lifetime , with a twelfth issued posthumously . All songs are copyrighted to Robert Johnson , and his estate .
Simplified: Eleven grammophone records were made by Robert Johnson with Vocalion during his lifetime , and a twelfth record was made once he had died .