How is "no longer on the market" defined by SE?

"No longer available" is designation supplied by Elliman--not Streeteasy. It would generally suggest apt. closed, but this cannot be confirmed until the filings appear in ACRIS--usually weeks after the sale closes. If the contract fell through and the seller withdrew the apt. from the market, the same designation could just as easily be inserted. Here, because of the 2-month span between contract and "no longer avail" it would strongly suggest a closing occured.

#14E did sell - there's a UCC1 on file:
http://a836-acris.nyc.gov/Scripts/DocSearch.dll/Detail?Doc_ID=2008103100776001

As kylewest noted, Streeteasy won't show the sale transaction until the tax statement comes through.

By the way, the Armstead is a very nice building. The "E" line isn't one of its better layouts, though.

Does thIS close not list what the property closed for?

The tax statement will show the price. The UCC doesn't.