Back in 2008 both 1719 and 1721 4th St were vacant properties. Recently 1719 4th St NW was sold for $682,500 in May or April of this year. Looking at the photos on the Redfin page for the property, it has been improved since it and the neighboring 1721 were highlighted in 2008 on the InShaw blog.
There is some history with 1721 4th St NW. I forgot when Mr. Hosseinkhani bought the property, but I did fight his zoning variance back in 2009. The first drawing had a pitched (suburban looking) roof. The roof was changed to the mansard roof, which blends the popup a bit better. It worked out. The concern I, and a neighbor who at the time lived across the street, was what impact would this have on the row of Wardman houses. This was a real concern with a vacant lot that is currently sporting new construction. After that the owner has been working on the property very, very, very, very slowly. About 4-5 years slow.
In that time, as far as I can tell, it was not charged the vacant rate, rightly so. If work is being done, then it technically isn't vacant. The work was done in drips and drabs. Nothing, then a lot of activity, then nothing, and some activity. Permits are one way to hold off the vacant tax rate, but those have limits. But permits with intermittent work seems to work in holding it off. 1719 4th St NW paid the higher rate for one year and that was 2008.
1721 4th St NW has been divided into 2 condos and both are for sale.