I'm struggling to understand how "quite a few people" thought/still think? such blood could be extricated from previously soaked garments, regardless of what the garments were. Eg, quite naturally, the garment, already having shed some blood content from having been soaked in water which may very possibly have had some sort of detergent added to it, would have needed to be dried prior to the removal of the 'material', after which the likelihood of collecting "a flake" becomes seriously diminished. Then there is the fact that dried blood oxidises very quickly and bears no resemblance to the "blob of jam" it was claimed to. Short of a family member having a Phd in science or being able to persuade a friendly scientist to do a bit of 'overtime' in a conveniently placed laboratory, I fail to see, without going into realms of the fantastic, how occurred anything like it.