I don't find it that hard to believe that no-one noticed when you consider that there are 57 episodes between Hind Sight and On a Wing and a Prayer plus the break between seasons filming schedules.
I highly doubt that RDA would misspeak his lines. He certainly wouldn't remember any details from 57 episodes ago so that can only mean that was the written line for him.
My initial reaction is that this isn't a big mistake, but I guess in the context of a clip show they should be taking care to get the details right. Having said that though, they are working on an 8 day schedule to produce an entire episode every 8 days, so if this is the biggest mistake we can find, they haven't done too badly have they?
Nice spotting on the nitpick though