As Tomaž Bratanič had answered, graph modeling depends on your needs(pattern of querying).
For example, tradeoff in detail:
Putting the SSN as a node/vertex will make the query pattern: Find vertices/nodes with certain SSN
easier as underlying it's a native graph query, where you are doing graph walk/traverse from a starting vertex/node.
Instead, putting SSN into different types of nodes/vertices(different labels/tags) as a property will make that query more costly in a graph database, where, it will scan nodes/vertices' properties(and if we index/make an ordered duplicated data for this to accelerate such query pattern, the writing path will be more costly comparing). The PRO of this property approach
will make the query pattern/partial query pattern of Fetch node/vertex properties
less costly.
One experience I also could share when designing the graph model is, to do it following your intuition(as graph model is intuitive). Revisit/revise it when your system involves.
Also, put some ref from Nebula Graph, the project I am working on ;)