If that card with is fingerprints was stolen from the FBI file, then yes, I agree it is an egregious error or leak and must be investigated to find out exactly how and who leaked it.
As for collecting Lennon memorabilia, I have a rather narrow view, given my present circumstances as to what is public info and should be the right of the public to hold and view and to own, and what is not.
I would IMHO defer to Lennon's children and his widow as to what can be owned of him.
But I do aknowledge that although I am not married to a public persona, there is the possibility that my spouse's death would be in the public realm for public consumption.
If, God forbid, that should ever come about, I would fight tooth and nail like a Momma grizzly bear(meaning I would be ruthless and take no prisoners and have no mercy) to protect what I consider sacred and that is my Husband.
JMHO and thoughts on the subject matter