BRUSSELS, Oct 16 - The euro zone's inflation rate remained unchanged at 2.1 percent in September, just above the European Central Bank's tolerance threshold of two percent, the European Union's statistics office said on Thursday. This confirms Eurostat's estimate from September 30. Compared with August, September consumer prices in the 12 euro zone nations rose 0.3 percent. The annual rate in August was 2.1 percent, the same as in August 2002, Eurostat said in a statement.//