I would suggest having the first of your scripts for each project copy the data from the central location, if the data is of a size such that it's feasible to do so. That way, your data can't change out from under you, but it's explicit where it came from and can be updated if desired.
For that script, an absolute path seems reasonable, as anyone outside of your organization won't be able to access it regardless, and anyone in the organization should have access to the given path. It would be similar to having a script that pulls data from a database prior to processing -- your reference to the database is generally going to be "absolute".