Near as I can tell, the AD&D Longsword is a gygaxianism. The German Langenschwert was intended for two hand use, being "longer" than other swords. Add in that the term "Broadsword" is closer to being a modern term than it is a medieval one (apparently first used in descriptions in 19th century collections) and we find the Gygaxian nomenclature probably had more to do with fantasy than fact.
This is not a complaint against the system. I would much rather write Broadsword or Longsword than scramanseaxe on a character sheet. Granted, Bastard Sword is the "original" name for Reahlyn's blade--a sword neither in the one-handed nor two-handed "families".
https://www.thearma.org/SwordForms.html Has excellent information.