The underlying models behind snapshots don’t change, that’s why it is called snapshot (and snapshot != fingerprint).
If you found that behaviour changed in the past, it might be due to code changes that affect the model’s output and it should be considered a bug, so if you have specific examples of this feel free to share!
The alias points to a snapshot, often to the latest but it can also point to an older one. The pointer can change over time, that’s why we say if you would like to lock in a specific version you should use snapshot names and not aliases.
Hope that clarifies things.
Also, wanted to let you know that the team has looked into vision cost calculation and it is indeed a little different than what is stated on the docs (the calculation is a bit more complicated than that), so we will update the docs to reflect the precise formula. Thanks!