I am resurrecting this request since we still get inquiries about supporting this…
TL;DR (from OP’s original suggestion)
I would say to not output the individual messages after a community mystery gift but some applications want to track who received a subscription from that person for statistic tracking, so maybe add a special flag to the normal gift sub message indicating if the gifted sub was a mystery sub or not (true or false) this way programs or services (like Alerts) only caring for the mass community mystery gift can ignore all following USERNOTICE messages that have set the mystery gift flag to true.
Would the best solution to this be rather than to add additional fields (and in the future features may be added/removed so would require changing tags each time) to indicate if a gifted sub was a mystery sub, to instead just add a reference fields that points to another id (in this case, the id of the mystery gift notification)?
This way with a reference you could easily know which subs are from which gift as they would all share the same reference, the message that they are referencing would have the details if it’s a mystery sub or not, and allow easier addition of new features in the future as none of us (or Twitch) would have to make any changes for the sub message code, we would just need to look at what’s being referenced.