Panini-sutra 3.1.95-132 prescribes krtya-suffixes: tavya, tavyaT, aniyaR, yaT, KyaP, NyaT. In 3.1.123, Panini enumerates 17 gerundives, which are taught as Vedic forms (chandas-). This sutra is especially important to consider the question: what Vedic texts did he exploit? It has been researched by P. Thieme, and yet there is room to reconsider his conclusion.
The term chandas- seems to be used in two senses. One is ‘Samhita’, the other ‘archaic language’ as opposed to bhasa- ‘common speech’. It is note-worthy that some gerundives enumerated in 3.1.123 are found only in Brahmana and Sutra literature. e. g. stárya- ‘to be laid low’ SB, unniyam ‘upwards’ SankhGS, and khanya- ‘to be dug’ LatySS-DrahySS. If the assumption that Panini quoted khanya- from LatySS-DrahySS is correct, it follows that chandas- also covers Vedic usages which sometimes appear in Sutra literature.
“...staryadhvarya...” in 3.1.123 should be interpreted as starya- + adhvarya-, and stárya- occurs only in SB. According to Thieme, starya- was abstracted from astarya- MS I 5.10:78, 11 on account of its irregular accent (cf. 6.2.160). But stárya- must have been taught by Panini as a Vedic word assuch, or an exception to 3.1.124: *starya-. Therefore, the question whether Panini knew the White Yajurveda needs to be further discussed.