For example, Thurgood (1994) examined Benedict's claims and concluded that since the sound correspondences and tonal developments were irregular, there was no evidence of a genealogical relationship, and the numerous cognates must be chalked up to early language contact.

[5] However, the fact that many of the Austro-Tai cognates are found in core vocabulary, which is generally more resistant to borrowing, continued to intrigue scholars.

There were later several advances over Benedict's approach: Abandoning the larger Austric proposal; focusing on lexical reconstruction and regular sound correspondences; including data from additional branches of Kra–Dai, Hlai and Kra; using better reconstructions of Kra–Dai; and reconsidering the nature of the relationship, with Kra–Dai possibly being a branch (daughter) of Austronesian.

[6] Sagart (2005a) cited a core of regular sound correspondences relating words belonging to the basic vocabulary in Benedict's work.

Ostapirat (2005) later presented fifty core vocabulary items found in all five branches of Kra–Dai, and demonstrated that half of them—words such as child, eat, eye, fire, hand, head, I, you, louse, moon, tooth, water, this, etc.—can be related to proto-Austronesian by regular sound correspondences, a connection which Reid (2006) finds convincing.

For example, the proto-Austronesian root *qudip "live, raw" corresponds to proto-Kra (k-)Dep and its reflex ktʰop in Laha, as well as Tai dip, all with the same meaning (the *-D- consonant is Ostapirat's voiced plosive of undetermined quality, probably alveolar as opposed to dental articulation).

From Indic borrowings it appears that tone B was originally a final h in Kra–Dai, and some of the corresponding Austronesian roots also end in h, such as AN *qəmpah "chaff", Kam–Sui paa-B (Mulam kwaa-B), though there are few examples to go on.

It may correspond to *H, a laryngeal consonant of uncertain manner, in proto-Austronesian (AN *quluH "head", Thai klau-C), but again the number of cognates is too low to draw firm conclusions.

Sagart (2019) finds multiple examples of the correlation between the coda of Proto-Austronesian polysyllabic words and the tone of suspected Kra-Dai cognates.

Lexical correspondences between Proto-Austronesian and Proto-Hlai, as well as Proto-Kra: Among scholars who accept the evidence as definitive, there is disagreement as to the nature of the relationship.

Benedict attempted to show that Tai–Kadai has features which cannot be accounted for by proto-Austronesian, and that therefore it must be a separate family coordinate with Austronesian (a sister relationship).

Sagart (2005b) suggests that Austronesian (including Tai-Kadai) is ultimately related to the Sino-Tibetan languages, forming a Sino-Austronesian family.