Your questions are very legit and you're not the only one having difficulties to grasp graph modelling at first ;)
It is always easier to start thinking about the questions you wanna answer with your data before modelling it up front.
Let's imagine you wanna retrieve the GDP of year 2012 computed by CIA of all countries.
A simple way to achieve this is to label country nodes uniformly, and set an attribute name that obviously depends on the country name.
Moreover, CIA/WorldBank/Government in this domain are all "sources", let's label them uniformly as well.
For instance, that could give something like:
(ORGANIZATION {name: CIA})-[:HAS_COMPUTED_GDP {year:2011, value:994}]->(COUNTRY {name:China})
With Cypher Query Language, following this model, you would execute the following query:
START cia = node:nodes(name = "CIA")
MATCH cia-[gdp:HAS_COMPUTED_GDP]->(country)
WHERE gdp.year = 2012
RETURN cia, country, gdp
In this query, I used an index lookup as a starting point (rather than IDs which are a internal technical notion that shouldn't be used) to retrieve CIA by name and match the relevant subgraph to finally return CIA, the GDP relationships and their linked countries matching the input constraints.
Although Neo4J is totally schemaless, this does not mean you should necessarily have a totally flexible data model. Having a little structure will always help to make your queries or traversals easier to read.
If you're not familiar with Cypher Query Language (which is not the only way to read or write data into the graph), have a look at the excellent documentation of Neo4J (Cypher: http://docs.neo4j.org/chunked/stable/cypher-query-lang.html, complete: http://docs.neo4j.org/chunked/stable/index.html) and try some queries there: http://console.neo4j.org/!
And to answer your second question, if you wanna add another year of GDP computations, this will just boil down to adding new relationship "HAS_COMPUTED_GDP" between the organizations and the countries, no more no less.
Hope it helps :)