The clearest way to see the difference is to look at what each number is for. The city sets a levy it needs to collect, then divides that burden across all assessed properties through mill rates, with a separate education portion. If every assessment in Saskatoon doubled overnight and the levy stayed flat, nobody's tax bill would change much. Value has moved; the tax has not.
That is why a rising assessment is not evidence your house gained that much, and a flat one is not evidence it gained nothing. What you should compare is your own notice against similar neighbouring properties, because being assessed high relative to your neighbours is the situation that actually costs you money and the situation an appeal to the Board of Revision is designed to fix.
Neither figure captures the individual house. Assessment works from recorded attributes, so a rebuilt kitchen, new shingles, an upgraded electrical panel or a basement developed without a permit sit outside it entirely, and every automated estimate drawing on the same records inherits the same blind spot. Joel Dyck's hand-reviewed valuation counts that work and prices it against sold comparables.