Disclosure: I build Schemity, a desktop ERD tool - this post is from our blog and uses it for the examples.
TL;DR: A diagram stored as a file is only version controlled if its folder happens to sit inside a Git repository, and nothing in the tool tells you whether it does - so the safest-feeling diagrams are often the untracked ones. Schemity now shows a Git branch icon beside every workspace that lives inside a repository, detected by walking up the directory tree so a workspace nested deep inside a project counts too, and marks imported workspaces with their own icon so the ones you deliberately placed inside a repo are distinguishable from the ones the app created for you.
A diagram is not under version control because you meant it to be. It is under version control if, and only if, the folder holding it sits inside a Git repository - and until now nothing in Schemity told you which of your workspaces did. Now every workspace that lives inside a repo carries a Git branch icon in the workspace list.
That sounds like a small thing. It is small the way a fuel gauge is small.
The assumption you never actually check
