DJPA treats the plural of this word simply as a form of pry in JPA (with much justification, also so for CPA!), but to judge by the existence of two clearly different forms of the singular in Syriac, as well as the appearance of clearly singular forms of this word in PTA, CPA, Mandaic and JBA, this has become a separate word in at least some if not most post-OfA dialects. In Babylonian it is probably the only form.
The situation is thus as follows: Prior to the later dialects, only pry, but unfortunately, there are no clear attestation of a plural before that time. In colloquial Palestinian dialects generally sg. pĕrī, sg. emph. pēryā, pl. pērīn with some contamination from Syriac and Babylonian in the texts; Syriac: both forms, but the meanings have been divided: this form is for the fruit of trees as well as figurative meanings while the form ܦܪܝܐ is used only in the figurative senses; Babylonian only pērā. LJLA appears to be completely confused, and identifying mss. that use the forms consistently should prove to be a useful indicator. KWIC searches should examine both forms.