I think Kim's approach is best, unless you need to have a bunch of programs. Just create one engagement program, with several streams, and you're good to go.
From my understanding, they can't be part of more than one stream UNLESS these are different programs. And you'd set up the transition rules between streams in one program so the lead would be moved at a certain point.
If they are different programs you could add filters like not member of -- (the program).
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