Thinking your borrowed disc is 'dodgy' is one thing. If a repair installation was done, then the verification of a genuine Windows Operating System would very likely have taken place in the process. If you now have a viable system that works OK then leave it be for the moment. If you get your automatic updates installing as usual then it would appear that you are using a 'genuine' Windows installation. If you get a warning in the future that it is not genuine, then you have your original disc to fall back on to make it so. The old rule of, if it doesn't appear broken, don't try to fix it.