[1] Ostapirat (1994a, 1994b) addressed issues such as breathiness and preglottalized nasals in Proto-Kam-Sui.
[6] Norquest (2021) reconstructs velarized consonantal onsets and retroflexes such as *ɭ in Proto-Kam–Sui.
According to Liang & Zhang (1996:25–29), based on evidence from Chinese written historical records, Kam-Sui languages were originally spoken in western Guangdong, but Kam-Sui peoples later started to migrate out of Guangdong during the Sui dynasty and Tang dynasty (from the years 600–800).
Sui and Maonan migrations were completed by the Song dynasty, around the years 1000–1100, while the Lakkia migrated to their current location in Guangxi from Huaiji County and Fengkai County, Guangdong during the beginning of the Ming dynasty (years 1300–1400).
Some Proto-Kam-Sui lexical items are cognate with Proto-Tai but differ in proto-tone.