If you are using RCE, Marketo will provide attribution when
First Touch (Acquiring Program)
any Program with a Success before the Opp Closes.
It only gets Pipeline Credit for Success BEFORE the Opp is Created.
So MQL really has nothing to do with this unless you are doing something else with the Team Generated stamp. But if you mean that the Lead does NOT exist in SFDC until MQL, then you would have to sync that Lead and get it on the Account to ensure full Marketing Credit. You will also need to set RCE to Implicit instead of relying on Contact Role (not reliable).
Please describe more about your setup if this doesn't answer your question.
The attribution calculations are not configurable in Marketo so you will not be able to grant partial credit in this case
For our marketing at Bizible, we generally keep marketing touches separate from historical stages. For example, if marketing had touchpoints on an opportunity it would still get credit, whether it previously went through MQL or not. It just matters if marketing influenced the opp/deal and, depending on the attribution model you're using, where in the funnel that influence happened.
We're always open to chatting more about Bizible and attribution, so feel free to reach out to us at http://www.bizible.com/contact if you want to geek out.