Complex sentence: These are the earliest photographs of the museum's collection, which was the most complete in the world at the time, and they recorded the fragments and scrolls before their further decay in storage, so they are often considered the best recorded copies of the scrolls.
Split into simpler sentences: These are the earliest photographs of the museum's collection, which was the most complete in the world at the time, and they recorded the fragments and scrolls before their further decay in storage. So they are often considered the best recorded copies of the scrolls.