The Treaty was signed in one day; it took a year to draw it up and decide on what it would contain. The Versailles, Trianon, Neuilly, St. Germaine, and Sevres treaties were all the result of the Paris Peace Conferences of 1919-20. As a result, in the case of Germany, the war did not technically end until the treaty was signed in 1919, hence the Blockade being maintained.

If you're looking for a good book on the subject, Paris 1919 by Margaret MacMillan is excellent.