The release date is the date when an Eamon adventure is first made publicly available for others to play. In most cases this is the date when the club (either the NEUC or the EAG) announced the adventure's release in its newsletter, and so is usually just a month and year.
Release date is not the same as creation date, and is usually somewhat later; for example, Margaret Anderson wrote and submitted Treasure Island sometime in 1991, but it was not announced until March 1992. Genz and Braun wrote adventures in 1981 that weren't formally released by the club until 2003.
The release dates for the first 37 Eamon adventures are uncertain since they were in circulation before the formation of the first Eamon club in early 1984, and no records exist to document when or how they were first made available. The Adventures Portal approximates the release date for the first adventure, The Beginners Cave, as late 1979 based on the research and rationales given by Jimmy Maher and Matthew Clark at The Digital Antiquarian. The dates for the remaining pre-NEUC adventures are approximated by year, but more precise dates for these are unknown.