For instance, electrons always move the same speed in a given metal. Which of couse isn’t even ‘true’ because temperature affects mobility.
There are multiple mechanisms for metal to migrate, grow whiskers, or whatever you like to call the individual growth on an object. I mentioned that in the case if ICs, we are concerned with one we call electromigration. I’m not saying all metal migration is due to electromigration.
You’re being pedantic when all I’m saying is, I deal with these sorts of concerns in my job.