As far as I know, we should add a verbal command only, when the dog has perfectly well understood, what we want from him and does it correctly (don't remember exactly) at about 98% or something around this. I'm using a verbal command meaning "go up to" for all the different items I use in order to generalize the exercise. They understand this command already since quite a lot of time.
The different items they have to step on I have not named yet, except the bed. I tried with 3 objects, but this still confuses them. So I now name until now only "bed" where they (provided I will succeed!) should stay for a longer period of time, e.g. when we have visitors and on other occasions.