https://www.rugbyleagueproject.org/seasons/nswrfl-1964/round-1/parramatta-eels-vs-canterbury-bankstown/summary.html
https://www.youtube.com/watch?v=fVOI5wtXAig
John Cox for Parramatta wore jumper number 5 in this match not 21 as can be seen at 4:14 in this footage.
Thanks Ted.
We generally assume a player played in the number they have been allocated in the program if they were a replacement in the starting team or came on during the game this seems not to always be the case as John Cox was a replacement in starting team for Mike Jackson and was listed in reserve grade in jersey #21 so we assume he played in #21.
It is impossible to know unless there is video of the game.
I totally understand. There isn't much option without video or if there are any club records they would grant access to which is highly unlikely.
Also to in regards to this Round 1 game between Parramatta and Canterbury in 1964.
-Brian Hambly had 7 Attempts at Goal.