As we upgraded DSS (twice) we noticed that the remote repository keeps old images. I believe this makes sense for clients that will eventually not redeploy API services or still keep some legacy job untouched after a deployment.
At Zip, in the two times we upgraded the platform, we also redeployed everything, thus making those old images totally unused.
Maybe, there could be a macro in the platform to eliminate old images (locally and in the remote repository) and also double-check they are indeed not being used.