It is happening at different levels. Sometimes I think it's happening because some organizations finish their data updates sooner than others. For example, the office of energy efficiency relies on StatsCan data, but StatsCan may update their data faster, so for the same oil consumption in one sector you will not get the same numbers.
A lot is also happening between provincial and national data sources. Sometimes it's even totally incompatible, not only in terms of energy but also in terms of emissions. The emissions inventory in Quebec is not at all the same as the Quebec portion of the “National Inventory Report”, so it becomes very difficult to try to match all of this.