How certain are we that the person putting together the pool will not collude with the providers of the elements to include bits-gold pieces that are fakes?
It’s based on strong security, minimizing trust, in sharp contrast to mortgages where one must trust all the parties involved, depsite the often bad incentives (moral hazard) involved. The title registry, which holds the timestamp hash chains, solutions bits, etc. is public — supply cannot be hidden. An overview of the security protocols involved is here (http://unenumerated.blogspot.com/2005/12/bit-gold.html), with links to further explanations.