I only run BiaB from the USB hard drive and always install the Patches to it.
Never a problem.
If there is some day, it's PG's responsibility to fix it.
BB always places the previous version in storage so that we have the option to Revert to the previously installed one in case something is horribly wrong with either a New Version or Update install. That said, in all these years I've never had to use it.
BTW, one of my long time pet peeves is the folder path questions in the BiaB prompts.
Ignore what is says logically and just replace "C" with whatever your USB drive letter is.
In my case it's "K."
With each New Release Installer, I've only had to reset that once, the first time.
After that, the Installers and the Updaters always open with those path settings remaining as I entered them. Your setup doesn't do that?
--Mac