Appraisal/Tax Record Issue

[Elizabeth Martin]

I've been reading and reading and haven't found a topic or google hit for my exact situation so wondering if anyone here has any insight...we are under contract on what was listed as a 4 bd/2ba home, and all 4 bedrooms are legitimate bedrooms under the Florida Building Code (over 70 sq ft, window, exterior wall, emergency exit, and they all have closets). None of these bedrooms were added on to the home at any point, it is what it has always been. We get the appraisal back and there is a $20k gap, we notice that that the appraiser has evaluated the property as a 3bd/2ba house which of course will appraise for less. We have escalated back to the appraiser to correct the error and are still waiting to hear back.

In the meantime, our realtor tells us that maybe the appraiser did that because a 3bd/2ba house is what is reflected on the tax records - and low and behold I pull up the tax records and it does in fact say 3bd and not 4bd. I am trying to understand - is the appraiser required to base the appraisal off the tax records or should/could he base it off what he saw with his own eyes - 4 rooms that are used as and qualify as bedrooms? 

I am hopeful the appraiser updates the appraisal and this is a non-issue but I'm trying to anticipate how it could play out if he comes back and tells us the appraisal has to reflect the tax records. We are supposed to close April 28 and of course the sellers trying to get the tax records updated and get it re-appraised in that time will not happen in that time frame. My other plan is tell them we'll pay the appraised price and take over dealing with getting the records corrected (but need to look into what tax liability there may be if the sellers were potentially underpaying on property tax for years because they didn't ensure the record was correct). 

Ultimately, we really close on this property but coming up with the cash for a $20k appraisal gap is out of the question so I'm thinking through all the possible ways this could play out! If anyone has any knowledge about whether or not an appraiser is required to base the appraisal off the tax records even if those records are incorrect, would love to learn more about this, or any other thoughts anyone has!