I'm upgrading my computer soon but I was given a System Builder/OEM license key and when I asked whether I could transfer the license the key to my new motherboard and storage drive they said I could using the "slui 3" + "slui 4" method to unlincense and license the key again. I've seen a couple posts saying that if you have an OEM key it is bound to the current motherboard you have and if you want to a free license you will have to buy the Retail key in order for it to be unlocked when transferring.
Edit: When I bought the key I wasn't aware that it would give me the System Builder/OEM key, it didn't mention anything about the key being OEM or Retail.