Complex sentence: Determining the identities of the few survivors of Chełmno had presented ambiguity because records used different versions of their names, and one survivor may not have been recorded in the early postwar years because he did not testify at trials of camp personnel.
Split into simpler sentences: Determining the identities of the few survivors of Chełmno had presented ambiguity because records used different versions of their names. One survivor may not have been recorded in the early postwar years because he did not testify at trials of camp personnel.