OK I'll chime in on this.
1. For my credentials on this topic: I was the first researcher to examine the Titanic's claims at the National Archives in Bayonne, NJ (having discovered them by pure accident, as a natural consequence of my Republic work - see Charlie Haas' and Jack Eaton's listing of credits in at least two of their books). White Star Line was protected by the Harter Limitation of Liability Act. See:
http://www.rms-republic.com/conceal04.html. So the only claims that would be filed within that action would be for un/self-insured items, of generally minimal value, particularly when compared to privately insured items. See for applicable argument:
http://www.rms-republic.com/other_cargos3.html
2. Insurance companies had no interest in filing their claims. There was no benefit to be gained. See argument, loc. cit.
3. Since, no doubt, the most expensive losses of cargo, jewelry, personal effects, etc. would have been privately insured - and, since there was no incentive for insurance companies to file a claim (there was no one to collect against - AND no insurance company did file a claim as a part of the Limitation of Liability proceeding), we can only speculate as to what may have actually been lost. Certainly, if we assume that the bulk of valuable passenger effects were privately insured, unless the passengers indicated their loss and their comments were reported within the press - the public wouldn't know.