For the Lakemaster chips (in Humminbird units) you can check to see the level of detail it offers for each lake or body of water. For example, Pokegama by Grand Rapids it shows that it is charted in HD and the survey was completed by Lakemaster themselves. Based on that, I’d expect to find accurate 1′ contours for that lake.
https://www.humminbird.com/support/chart-lists
I will say that some of the depths are off at this time because of a major drought though. Everything was about a foot or a little more off for most of the past open water season. That problem exists with every mapping software though.
I can’t speak from experience on the Lowrance units, but for the Humminbird/Lakemaster chip combination you can adjust the lake depth and it will change the contour lines displayed on your map. Note: this is adjusting the contour depths, not your sonar depth readings (which is a separate thing you can also do). On LotW this fall I changed the map by -2 feet and the contours nicely matched up to what we were seeing on the sonar.