I'm looking for wisdom on the drastically different elevation changes I see post-ride on the various hardware & apps I'm using. I typically use a Garmin 200 Edge to track my rides live, then Garmin Express to upload the file to Garmin Connect, where I also have it set up to send to Strava and Map My Walk (using just because I have legacy workout files there). I'm finding that the elevation change reported on each of these is wildly inconsistent. I do understand the Garmin's "elevation corrections" feature, which allows you to either use the Garmin's own raw data or enable elevation corrections, which supposedly cause the elevation to be calculated from professional land surveys. Even accounting for that feature, the elevation reports I'm seeing are wildly inconsistent.

Here's an example of elevation reported from a ride I recently did:
Garmin Edge 200 elevation reported, with elevation correction disabled = 1,483 ft
Garmin Edge 200 elevation reported, with elevation correction enabled = 811 ft
Strava elevation = 1,137 ft (which is odd, because the file came directly from the Garmin software)
Map My Walk elevation = 927 ft (again, very odd because the file comes directly from the Garmin)

I even went into the Garmin elevation profile for the ride and counted up each individual hill's elevation change (a mind-numbing exercise) and got over 1,700 ft of climb.

Any thoughts on why these are so different, and which is likely to be the most accurate? Thanks