I have 4 files:
they are added to bundle in following way:
bundles.Ad
Your actual question is not answerable because it is already acting as documentation states (which is why I asked what documentation you were looking it, but you have chosen to ignore my comment).
If you want to keep the same behavior in release mode, use BundleTable.EnableOptimizations = false; in your Global.asax. This will turn off the bundling and minification that is active in debug mode only. Then to use your own minified css / js files, simply point your bundles path to the minified versions.
According to documentation, you could also use "~/Content/a{version}.css" which would use non-minified version in debug mode and minified version for release. However, I have not tried that.