We're talking about
Enchanted or Imbued Elven Chain items. The Dark and Half Elf variants were Enchanted/Imbued Teir`Dal Chain.
Early posts on Allakhazam regarding these combines come from the Feb/2001 era, which gives us a rough date of introduction circa Velious. Further research yielded
this web archive of Everlore, with commenters from October/2000 (post-Kunark, pre-Velious) speaking of the Enchanted combines.
Through this research, we can ascertain that the first combines were introduced with Kunark. Later comments suggest that the complete details surrounding these elusive armor sets were not finalized until mid-2001 when the Enchanter's "Enchant Mithril" spell was introduced, which obviated the need for planar-sourced Blue Diamonds and opened the unknown recipes for experimentation.