It would be helpful for us to answer your question more specifically if we knew the basis from which you are coming from. Because as many other professionals have stated, the list price of a home does not dictate the final sales price and final sales price does not necessarily impact the tax assessment of a neighboring home. My answer is based on the assumption that you are hoping your taxes go down if the property is sold for $200K less.
There are many factors that affect the assessment value of a home I will provide you with a link so you can look up some of them which have already been stated, like square footage, # of bedrooms, etc, etc please see here for additional information http://otr.cfo.dc.gov/otr/frames.asp?doc=https://www.taxpaye
If you were to look at tax bills now, you will see they vary somewhat in your neighborhood already, given the fact that Chevy Chase itself is a community in DC where homes have many unique characteristics and without an interior inspection one will never know. Tax values are generally based on the historical reported information (i.e. permits, etc) and the exterior of the home and not on any improvements that can be quickly observed from the outside (like a finished basement).
Additionally, DC has many Tax Relief programs and Tax credits like the Homestead Exemptions, Historic Tax credits, Senior and Disabled, etc...so as you can see, a little homework can go a long way in maximizing all the credits you can take advantage of in the District and the other option you have is an assessment appeal.
Also, please note that it depends on when your home was purchased as to how it affects your tax bill because there is an annual cap on taxes regardless of what the values of the current sales prices are in the community.
I hope this helps and is what you were looking for in terms of an answer and pointing you in the right direction of understanding a little bit about tax assessments!