It may be possible to confirm family relationships by comparing test results with Bob or other carriers of his ancestors' Y-chromosome or mitochondrial DNA.
Y-chromosome DNA test-takers in his direct paternal line on WikiTree:
Y-Chromosome Test 111 markers, haplogroup I-M223
Mitochondrial DNA test-takers in the direct maternal line:
Family Tree DNA mtDNA Test Full Sequence, haplogroup H1a4, FTDNA kit #B5977
It is likely that these autosomal DNA test-takers will share some percentage of DNA with Bob:
AncestryDNA, GEDmatch A091116[compare], Ancestry member rdcarson58