A lead can only belong to one segment within a segmentation. It can can qualify for all segmentations. If it doesn't qualify for a specific segment in a segmentation, it will be part of the "default" segment within that segmentation.
If I understand correctly - In your NY/RI example marketo would move the lead to RI once the nightly batch runs. The only time Marketo will use alphabetical is when the lead qualify's for 2 segment rules. In this example it would be impossible because you can't physically live in 2 states.
My example on a base level doesn't seem possible I know. However I work in the insurance industry so it is not uncommon for someone to have multiple (for example) auto policies in multiple states. We record their Policy State info within a field called Garaging State, which lives on the Opportunity in Salesforce.
The Segmentation we have setup is based upon this Garaging State; if state = the abbreviation, its places under that state's segment. So in my world it is not uncommon for a customer to have an Opportunity with a Garaging State of RI and then later have an additional Opp with a Garaging State of MA.
We carry over 10 carriers in almost every state, so using Segmentations and Snippets for content is something we need to do to be more efficient. So if my email has a Snippet based on the Garaging State Segmentation and we have customers with multiple Opportunities with varying Garaging States, my snippets/segmentations do not populate correctly due to the ABC Segmentation issue.
Hope this clears up any confusion!