Complex sentence: Since October 15,1885, the name "Lethbridge" has been the official term; although the name Lethbridge was in common, if unofficial, use for the river bottom community at least as early as May 1884.
Split into simpler sentences: Since October 15,1885, the name "Lethbridge" has been the official term. The name Lethbridge was in common unofficial use for the river bottom community at least as early as May 1884.