The Sebring that have turend up so far have been Giant built models, circa 1983. This does not follow the Giant format of the era and suggests 1977 or 1987 but the model was not produced, or at least not cataloged, during this period. Alternately, the format could be interpreted as 1984. This is a case where photos would be a big help, since we haven't seen this format previously. You can also check the components date codes against the information on the components page of the Vintage-Trek website.