As part of Dr. Noonian Soong's work, Clendenning was one of many colonists whose experiences and memories were partially implanted into Data. This included experiences Clendenning had not been yet able to record.
By 2368, Kila Marr was familiar with his records, but had never read about the gamma scans. The knowledge of his work made it possible for the USS Enterprise-D to detect the antiprotons the Crystalline Entity left behind when travelling through space. (TNG: "Silicon Avatar")