License Key on upgrade to version 3

I upgraded to version 3, then went into version 1 and was told my license key was inactive and I was put in trial mode on version1.
I have a WIP that I may keep in version1 and had seen others being able to have both ver1 and ver3 running.

Is it safe to input old license key back into ver1, or will that deactivate the key in 3?

Yes. I have both versions running on my PC.