When presenting any type of evidence which could easily be hidden/removed through what ever means.. You should provide backups to the evidence provided. You can do this by archiving the post in archive sites. Screenshots aren't generally considered proof.

For example, archiving this thread before I submit this post: https://archive.fo/AZPh2

As you can see it takes a copy of the webpage at the time of archiving it. Any changes will not show up on the archive copy.