The City layer is accurate to 1–5 m, and 8.8 km of the untraced length sits 15–25 m from an OSM line, so the honest figure is ~60–75 km; 50.7 km has nothing within 50 m. The original audit's “OSM has 92%” divided total lengths — it never asked whether they are the same sidewalks.
Contains information licensed under the Open Government Licence – City of Guelph. Source: Sidewalks.