Well, in dev mode, it is concatenated only, not minified, so that's a little easier.
We used to keep files separate, but that ended up causing issues that would only occur on production, so the decision was made to keep dev and production mode similar except for crucial differences (e.g. minified vs not minified).
As of last year there was an outstanding issue with the version of uglify-js we use, in that there's no
.map file generated that we can use. I don't quite know how to resolve that yet... perhaps it has been fixed now.