The 1975 first began at Wilmslow High School, Manchester, playing together as teenagers in 2002. They performed under several different names before they signed with their record labels as The 1975 - such as Me and You Versus Them, Forever Enjoying Sex, Talkhouse, The Slowdown, B I G S L E E P, and Drive Like I Do.
They have lots of unreleased material and old versions of songs they re-made for their debut album and EPs - "Ghosts" is one of my favourite The 1975 songs, that they wrote as B I G S L E E P but that was never officially released. You can find the song on YouTube that someone uploaded with permission from the band's manager, as well as lots of their older stuff, like an original version of "Robbers" that's slightly different to the one they released on their debut album. Another one I like from before The 1975 is "Lost Boys", that they wrote as Drive Like I Do.
Just go and search YouTube for their more recent previous band names and you'll get results of their older songs that they didn't release ;)