at the risk of sounding defensive of my suggestion, I will offer one more piece of advice:
version control is more useful than you might think. Being able to go back and easily see what you changed between a version that worked a week ago and one that is broken today but is 5 revisions removed... super useful. Also, the version control mechanisms allow you to maintain versions of other peoples' code. I thought that might be useful to you since you mentioned that you're using "backlevel libraries".
Last but certainly not least, the control mechanisms I mentioned excel at maintaining code in multiple locations, not just in multiple versions. On windows, a simple right click->update on the folder you need to update (like My Documents\Ardiuino) will retrieve the latest revision from the server. Similarly, if you want to use an older revision, the process is maybe one step longer.
Using mapped network drives or google drive or any shared-location-without-version control is not only inelegant but runs the risk of fubar'ing the whole code repository. Using a version control system gets you all the benefits and simplicity of the other systems but *with* the added protection and organization of version control. I'll stop trying to convince you now... but I hope you give it a try. you will not be disappointed
