Since steeping is a sealed bottle sitting for a period of time out of sunlight, it probably won't need to steep more after nicotine is added..... Unless you have one of the non-typical mixes that jump starts the nicotine oxidation and the nicotine oxidation is key component of the notes that mean "fully steeped" to you.
If you are confusing steep with airing-out or breathe, which is an open bottle sitting for a period of time out of sunlight, and since one of the points of doing this for a period of more than a day is to get the nicotine to oxidize and add that bitter note, then airing-out a non-nic mix will not have the same results as doing so with the nicotine in.
I also noticed the same question was posted to Ask The Veterans. (Ask The Vets is always slower than asking in the open forum due to us Vets having to come into the hidden section and answer the transferred questions.)