Some languages (PA, PD, PL) contain the final labial *-b- which is obviously an original plural suffix (there is no trace of it in the PC and PWC forms). The strengthening *ʎ > *ʎ: in PWC is in this case possibly related to the loss of laryngeal (the presence of which is confirmed by the PC and PD forms); regularly we should expect a weak *ʎ (the vowel is short in PEC). Besides, the EC evidence points to a front *e vowel in the root, while in WC there is no palatalization. Maybe we should reconstruct some vowel variation in this root for PNC. In any case, the common origin of the word for 'three' in PEC and PWC is indisputable.
See Trubetzkoy 1922, 238, 243; 1930, 274; Абдоков 1983, 154.