Mattermost tested and found that when editing messages, it may not be labeled as a. This can be misleading when read messages after a certain time. It is impossible to say exactly what was written in the message so that the user can edit it. 
It would be great if you edit the message would be labeled as anything.
Thanks @danilvoe for the feedback!
We have an open JIRA ticket to add an (Edited) label next to the post if it has been edited at least once.
Wondering if someone on your team would be interested in contributing the improvement?
By the way, Holiday Hackfest started on Dec 8th, which is an excellent opportunity to win an exclusive Mattermost shirt by contributing to the open source project: https://about.mattermost.com/hackfest/