Creators can revise their artwork, so a downloaded thumbnail is a snapshot rather than a permanent promise about what the video will display. An archive should preserve that timing.
Confirm the source
Check that the old and new images belong to the same video identifier. Similar titles or reuploads can lead to a mistaken comparison. Record when you retrieved each file.
Keep both versions when relevant
If you are studying changes or maintaining a publication history, save the images under separate dated names. Do not overwrite the older file before deciding whether its historical context matters.
Use the right version for the task
For a current reference, verify the latest visible artwork on the video page. For a historical analysis, describe the time period attached to the saved version. Avoid claiming that a change caused a performance difference without appropriate evidence. The files establish what the artwork looked like, not why an audience responded.