Hello Gina! I think in terms of inbound volume, your logic is sound. The sum of all callbacks offered + sum of all voice offered - sum of voice flow outs would net you the total amount of call/callback inbound volume based on your flow design.
It's important to note that in general this formula isn't applicable for all scenarios. A flow out is a call that was waiting in queue and stopped waiting in queue for any reason other than the caller hung up (abandon). Some customers may use an in queue call flow to transfer to another queue and that action would register a flow out. Some customers my refer them to an online portal and transfer the call to a disconnect action after the customer confirms they'll follow up online. Many use cases can stem from an in queue call flow being used to send the customer somewhere else and that somewhere else isn't always a callback.
Sounds like you're using flow outs exclusively to mark calls that got transitioned to callbacks. As long as that's true, your formula will work. For anyone else reading this, evaluate your call flow because your situation may be different!
------------------------------
Ryan Legner
Staff Product Manager, Genesys Cloud CX
------------------------------