Can we draw the following hypothesis from the context? 

Context:

Sparta is an American rock band from El Paso, Texas, formed in 2001. Founding members Jim Ward (vocalist/guitarist) and Tony Hajjar (drummer) are also members of post-hardcore group At the Drive-In. Keeley Davis (guitarist) is the former frontman of Engine Down.

Hypothesis: Sparta's songs are all written by Jim Ward and Tony Hajjar.
It's impossible to say