Depending on the location, we use recent information from the FAA or Nav Canada.
For the FAA we calculate if the value is older than 2010, since there's a lot of old data there.
For NavCanada we use the data supplied from them.
For international airports or situations we don't have magnetic variation, we calculate it internally.
For VOR's, the original declination is used (Variation of the VOR at the last or only adjustment).
We then do a dynamic calculation of Magnetic Variation as a route is planned. This means Magnetic Variation is very current based on a model for the current date.