He has recently been identified as Giuseppe Giovanni Battista's son and consequently as Andrea's grandson. De Piccolellis, the Hills and Santoro formed the hypothesis that he was the son of a Giovanni Battista Guarneri that lived in Saint Donato parish. This two different hypothesis of his parentage come from the parish register of Saint Prospero from 1731 to 1737 (published by the Hills), where Caterina Rota's husband Giuseppe Guarneri was registered as the “quondam” (deceased) Giuseppe's son, but Giuseppe Giovanni Battista, who was Andrea's son, was still alive in 1739. This discrepancy was probably due to a repeated mistake of the priest or of the person who wrote the register. Nowadays, many authors refuse the hypothesis of his origin in Saint Donato parish. Moreover, Giuseppe Guarneri, living in Saint Prospero parish, appears in 1740 in a notary deed with his brother Pietro, who was living in Venice. A legend tells that Giuseppe Bartolomeo was imprisoned for some years because of an unclear crime, but at present there is no documentary evidence of this fact.
After his death, in order to distinguish him from Giuseppe his father, the collectors of his instruments started to call him “del Gesù” because of the acronym JHS written on his labels: these letters, that are an abbreviation of his name Giuseppe, remind the acronym that refers to the name of Jesus Christ in the christian tradition.