Short answers, pulled from the story.
The first published Dungeons & Dragons scenario appeared in 1975 inside the Blackmoor rules supplement. This early text was titled Temple of the Frog and served as a guide for managing player activities within a specific scenario.
The very first stand-alone adventure module actually hit the market in 1976 under the title Palace of the Vampire Queen. Wee Warriors published this work while TSR distributed the first three printings on behalf of their partner company.
Steading of the Hill Giant Chief became the first stand-alone module produced directly by TSR in late 1978 after serving as an Origins '78 tournament module. TSR Hobbies published six adventures that year which had previously existed only within gaming convention settings.
All Dungeons & Dragons modules until late 1994 carried an alphanumeric code consisting of one letter and one number. The coding system was dropped altogether by the end of 1993 after decades of use across multiple product lines.
In 2008 the adventure code returned with the release of H1 Keep on the Shadowfell for fourth edition Dungeons & Dragons. This marked a revival of the alphanumeric coding system used to identify products by their sequence number.