I believe you to be correct in that POST was not an available HTTP method before HTTP 1.0.
Its definition in RFC 2616 may be found here: http://www.w3.org/Protocols/HTTP/1.0/spec.html#POST
While the following link suggests it not to be available in HTTP 0.9 (which was only given a version number after the adoption of HTTP 1.0) http://www2.themanualpage.org/http/http_http09.php3