An organisation wouldn't normally have documentation expressly disassociating itself from another, and it's highly unlikely that either Celtic or Celtic Boys Club did.
Perhaps more importantly, no paperwork that shows that their clear and obvious relationship was a contractual one has emerged - at least not publicly - emboldening Celtic in its 'separate entity' defence.
However, as Spotlight has revealed, there is a mound of evidence which proves that, in practice if not in law, Celtic had significant control of and responsibility for the Boys Club - sufficiently significant to make vicarious liability for the crimes of the latter's officials a charge that may stick.
Celtic has rather condemned itself, since page after page of the club's own newspaper once trumpeted the relationship and Celtic's pride in it. Only when the sexual abuse at the Boys Club became undeniable did Celtic decide to distance itself, to the point, apparently, of paying the Boys Club to change its name.
How things pan out legally remains to be seen, but whatever the law of the land might decide, Celtic will forever be guilty of allowing, even facilitating, the sexual abuse of minors on a scale unparalleled in the history of sport worldwide.
If you know your history then, indeed, Celtic are a club like no other. To its eternal shame.