Lead stages, and which ones are terminal
Six stages take a contact out of the calling list. Knowing which six is the difference between a clean pipeline and a mystery.
Lead stage is the highest-consequence field on a contact, because two things read it automatically: the calling list, and any campaign whose audience filters on open stages.
The division that matters is open versus terminal. Open stages mean there is still something to do by phone. Terminal stages mean there is not, and a contact in one leaves the calling list without anybody maintaining a suppression list.

Steps
Understand what a stage claims
It describes the person over their lifetime, not what happened on one call. That distinction is what keeps the field meaningful.
Learn the open stages
New and Contacted are the everyday ones. Anything that is not among the six terminal values counts as open.
Learn the terminal ones
Those six. A contact in any of them leaves the calling list, because there is nothing further to do by phone — whether that is because you succeeded, failed, or must not call them.
Treat DND as final
It carries legal weight in most markets. Moving somebody out of DND should be a deliberate, evidenced act — never a side effect of an import or a bulk edit.
Let outcomes move stages where they should
The outcome table already does this. Building workflows that duplicate it gives you two mechanisms fighting over the same field.
Check the stages match how you actually sell
Do this before go-live. Renaming what a stage means after six months of data is painful, and reporting across the change is close to impossible.
Use the segment chips to check your shape
The counts across the top of Contacts are a pipeline snapshot. A large New count with a small Contacted count means leads are arriving and nobody is calling them.
Check it worked
Look at the DND / invalid count. Then filter to it and read a few records. Every one should have arrived there for a reason you would be comfortable explaining.
The parts people get wrong
- Because the calling list is derived from open stages, terminal outcomes act as an automatic suppression list. There is nothing separate to maintain.
- Stage changes are audit entries on the activity feed, so you can always see who or what moved somebody.