One moment there are no "continuous jams". Each jam that repeats several times are separate jams with just similar names and often created by the same people. They aren't linked with any metadata or logic.
So it could be implemented via notifications that tell you that person you subscribed created jam. (I don't if it isn't implemented but while I read this suggestion I think not)
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Maybe somewhere internally the "continuous jams" exist but for what reason and how we could know...