The clarification comes in, to my mind, with regards to bringing together pieces from all 3 of the AD&D book into one place (e.g. halflings get +3 with missile weapons from the MM). OSRIC is an example of good archival research and best-effort at reading original intent, IMO. I haven't found (except for some missing stuff, like WvsAC) anything significantly different. They are, to my mind, the same thing---with a nod and wink that says we left some things out because of legal concerns (which subsequently proved to be minor). Those elements seamlessly stitch back in if you get the original books (now available, but weren't at the time of OSRIC's publication).
@Malrex & T1T: Eat your vegetables every day boys so your games grow up big and strong...and then, maybe later, you can have some candy.