This article examines the origin of the Can surname in several localities of Doai region by distinguishing three levels of evidence: verified data, plausible inference, and hypotheses that remain open to further verification. The applied sources include Vietnamese historical records, official administrative data, geographical gazetteers, Chinese texts concerning the characters艮,良, and 梁, and local primary sources that require additional examination, such as genealogies, village legends, cadastral records, inscriptions, royal ordinances, and ritual documents. The analysis suggests that, the hypothesis of a surname change from Luong to Can is historically and graphically plausible, especially if Luong was written as良. Nevertheless, the hypothesis is not yet supported by direct genealogical evidence. The stronger conclusion is that the Cấn surname became durably localized within the village society of Doai region. The article therefore proposes a next stage of verification based on local Sino-Nôm texts and lineage records.