This is frustrating for buyers and Realtors alike. Mistakes happen but some agents just copy the previously listed info which could have been wrong. Some sellers may not have reported a renovation that maybe didn't have the proper permits pulled (which may cause taxes to go up) and just gave the agent the original description. Short of measuring it yourself (which is recommend when making a purchase) the county records sometimes has a more accurate description. Again, that is unless there were any renovations that added or took away and it wasn't reported, otherwise they may have the original description as well.
You are wise to question these inaccuracy's. If the correct permits were not pulled and you bought the home you may inherit some headaches you didn't want. Not sure if this answered your question or not, but I hope it gives you a little insight as to what may have happened. Take care!