It depends on the track. If you have more specific tracks, send them to the best one.
it sounds like you need to create a traffic cop system that takes in leads for nurturing and decides which Engagements the lead should go to.
The rules will be yours. for example:
If Lead is VP of Tech, send to Senior Tech Engagement as long as Lead is Not already in any other Engagement. If so, then remove from other engagement and put in Senior Tech.
In Marketo that might look like:
Trigger: Job Title is now VP of Tech
Flow: Is lead in any other Engagement? If so, Remove froM Engagement X, put in Senior Tech. If not, put in Senior Tech.
This is not super easy to get right if you have several Engagements, but that is the general structure.