YR7 had a couple of helpful posts a while back trying to make sense of the original research rules:
These rules have caused a fair bit of confusion, and - short of clarification by the powers that be - exactly how to use them correctly will probably remain open to debate.
As for your specific question, I believe the errata slightly affect the premise upon which your statistics are based. As far as I can tell, the gist of the errata is: "Roll on the Extraordinary Results table. Add your risk modifier (+2 in your case). Apply the indicated result. Then (as long as you don't botch or get a complete failure) add or subtract up to your risk modifier to see if you can get a discovery result in addition to your first result."
That interpretation gives a slightly greater than 50% chance of a discovery on a risk modifier of +3. With a risk modifier of +2, I believe you have a 31.1% chance of a discovery. That is, you get a discovery on an unmodified roll of 7, 8, 9, 1-4, or 1-1-2 on the Extraordinary Results table. Add your risk modifier of +2, and these generate 9 (special/story), 10 (discovery), and 11 (modified effect). All of these are within +/-2 of 10, granting a discovery in addition to your first result.
(Rolling a six would result in an 8. While this is within +/-2 of 10, it's a complete failure and unfortunately doesn't count. I take it that if you rolled an unmodified 10 you wouldn't actually get a discovery, you'd merely get more rerolls, but that's open to dispute.)