While ASCAP credits Styles with songwriting on 40 registered songs, these new four are his first songs filed with him as the performer. All of his other work has been performed by One Direction, with the group listed as the artist on the track. There is not information included on any release date or plans for release at all, simply that these songs do exist and (most likely) in a recorded state.
ASCAP is a performance rights organization that collects royalties on behalf of songwriters and publishers for music played on television, radio, in stores, streamed digitally, performed live and more. All artists who wish to receive such royalties for their music must register their songs with one such agency. Styles' actually belongs to the UK copyright collection society PRS for Music, but that agency only releases information to users, while the American counterparts ASCAP and BMI allow the public to view it. (These songs do not currently show up on BMI's registry.)
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Styles' songwriting partners on these songs were Johnny McDaid of Snow Patrol and Gary Go, with the copyright split in thirds suggesting equal roles in the tracks' creation. Kobalt Music is currently listed as the songs' sole publisher; the company represents Gary Go's songwriting work.
Perhaps most importantly, it is worth stating that these songs may never actually be released. That they were registered tells us "5378 Miles," "Already Home," "Coco" and Endlessly" were written and recorded in some form, but whether that means they are fully finished and mastered is not clear. At most, this is proof of their existence and assurance that if they are released the songwriters will see compensation from public performances. Still, it does provide the slightest insight into what will come next and that we can likely expect a Styles solo career soon enough.