Stand Back promo 45 - can anyone help?

[Dodfather]

Hi guys

I recently picked up a Stand Back 45 that, according to the sleeve says that Garbo should have been on the B-side. However, Stand Back is on both sides! Both sides of the record say Stand Back and also "Promo copy - not for sale". I'm really happy with it, plays well and have no complaints, but I'm just wondering if anyone can tell me what it is I actually have? Was there a promo copy sent to radio? My guess is that this is the case and somehow over the years it's wound up in the wrong sleeve?