I mean if you only use one icon you can reach out to me via E-Mail and we can agree on something.
Generally let's say you make "legend of the warrior I" and you use i dunno 20 icons and then you make 2 prototypes for the next game, which you don't release but play around with, for those you can still use the icons, as you won't release it it doesn't matter.
But then at some point you earnestly work on "legend of the warrior II" in which you use the same 20 icons and 40 more bc. you reuse code and add features, then it's time for another license.