Deagol posted a correction to the IPL interview article - the copyright date for "Bilbo's Last Song" is 1976, not 1977.

Hugh's memory is not precise on dates, and detailed records don't exist any more, so the 1977 date was derived from the fact that the "Map of Middle-earth" puzzle is copyright 1977, and has an item number of 96T121 (the last three digits being the catalog number, which increased every time a new puzzle was produced.) The item number for "Bilbo's Last Song" is T128, so it was theoretically released much later. But all of my copies also have the copyright date of 1976. Have to go with the 1976 date, as that is the only official record remaining!