Will my Decoherent engrams ACTUALLY decrypt into Day 1/Year 1 legendaries?

Hello Guardians. I've been grinding the hell out of lvl 28 Prison of elders the past month and I've been saving up all of those lovely Decoherent engrams in the hope that they decrypt into old legendary gear. Being a day one player, having another shot at getting infamous auto rifles such as the 'Do gooder V' and the ORIGINAL 'Grim citizen' is very appealing to me but am I right in believing that I can get gear as old as those two or am I mistaken and I am only able to obtain legendary weapons from as far back as the House of wolves DLC? Please can someone clarify this for me and probably a lot of other guardians hoarding these engrams in excitement of getting one of these weapons. It's just the youtuber Rick Khakis posted this video stating that I could obtain the 'Up for anything' auto rifle from these engrams which has now made me rather suspicious.... (The video: https://www.youtube.com/watch?v=jXqz5HzdlEc Skip to 5:35)