By the time Jesus says:
Μὴ νομίσητε ὅτι ἦλθον καταλῦσαι τὸν νόμον ἢ τοὺς προφήτας· οὐκ ἦλθον καταλῦσαι ἀλλὰ πληρῶσαι (NA28)
“Do not think that I have come to abolish the law or the prophets; I have come not to abolish but to fulfill" (NRSV)
in Matthew 5:17, Matthew has used πληρῶσαι six times to show how Jesus has fulfilled what came before. Interestingly, though, Matthew only mentions prophets (five of the six uses before Matt. 5:17) and not the law per se. All the same, the listener/reader is likely thinking of the uses in the book so far when Jesus talks about fulfillment in 5:17 (as he did also in 3:15 at his baptism).