Velvia is a professional emulsion released to the market very close to its optimum palette and refrigeration (below 15c) for short term and freezing for long term storage is the prior-use standard. Any film that has been lying around unused, exposed to varying tempertures and climate extremes over a long period of time (and 2000 is a long time ago) will exhibit gross loss of film speed and contrast, colour shifts and casting (in Velvia 50, this is green but can also manifest as purplish). The rolls you have might be good for an experiment or two to prove Velvia's tolerance over time to degradation.

Presumably you are referring to Velvia (known as nothing else), prior to Fujifilm's tweaking of the emulsion and renaming it to Velvia 50? The former went out a long time ago so getting a data sheet could prove challenging. You could use the Velvia 50 data sheet as a start to experiment (rather than commit serious work to). Other than that, I'd toss it.