While looking back over HTTP response codes today I noticed that the 301, 302, and 304 response codes were defined in HTTP/1.0 but not the 303 response code. Does anyone know why the number 303 was skipped in HTTP/1.0?
It was not skipped right away. As you can see in this diff between version 1 and 2 of the RFC draft they dropped it. At the beginning it was in there.