The system-msg doesn’t contain the cumulative months if the streak is not shared:
msg-id=resub
msg-param-cumulative-months=45
msg-param-months=0
msg-param-should-share-streak=0
msg-param-sub-plan=Prime;system-msg=tduva\sSubscribed\swith\sTwitch\sPrime.
In webchat:
tduva subscribed with Twitch Prime. They've subscribed for 45 months!
It would be nice if this could be fixed and show the same thing as in webchat, otherwise the system-msg for this can’t really be used for output.