Although the other agents are right about the tax record, I believe your info is pulling off the MLS system from the listing when you bought the home in 2009. (It was 5BR in 2003.) Agents enter almost all the info on MLS except location and total s.f. Legally, NV RED requires MLS list a bedroom as having a window, a closet, and a door. Otherwise, it is considered an office, den, loft, etc., (rooms which Trulia currently ignores.) If the prior listing agent was incorrect or you remodeled, without relisting your property and it still really bugs you, you can try and call GLVAR directly and have the MLS dept make the correction, although they might not deal with the public. 702-784-5000 But you do have the 2003 MLS in your favor for an easy fix. However, your overall property values are more linked to overall square footage and an extra bedroom might bump you $1,000 on an actual appraisal, keeping in mind that I'm a Realtor, not an appraiser. There is a comparable home for sale right now on Mt Creek for $950,000, compared to the Trulia estimate. Both are simple guidelines without paying for an appraisal.
If I'm wrong and you actually need/want to call the CC assessor, they won't do anything without an appraisal, so in my book you'll be spending $500 to gain $1,000.