The gap is 22-24mm. Yes, it is as simple as that. Just keep in mind that a 2mm difference at the wide end (and 22-24mm is wide) is a much bigger relative framing difference than at the tele end. For example, the difference between 10mm and 12mm is a large field of view difference, while the difference between 280 and 282 is practically unnoticable. So yes, the focal length difference really is just 2mm "wide". Bit the impact of those 2mm to framing is bigger at the wide end than at the tele end. How big? I believe just doing a fractional comparison of the mm difference works here. 10mm is 2mm wider than 12mm, which is (2/12)*100 = 17% wider. But 280mm is only (2/282)*100 = 0,7% wider than 282mm.
Not entirely sure if that's an entirely valid calculation, but it's a fact that the relative framing difference is a bit bigger at wide ends. 22mm would be 8% wider than 24mm.
Also, sometimes the lens' "actual" focal length might differ just a tiny bit from the official spec. A reported 17mm is sometimes closer to 16mm (Tamron 17-50), for example. In other words, the reported focal length isn't always bang-on. But that's not a maths thing, just something to do with how they're physically built.