Paying close attention to what BB and their agents have posted in our forum's over the years we see that they are using a hardware random number generator as opposed to a software one. My research into that particular form of hardware generator has revealed that the experts are skeptical about the amount of randomness actually generated, some models fail the tests. This means we have a right to be skeptical when BB say it's fixed. This puts them in a bind, if they reveal the model and origin then there is a danger that we can use that to defeat the random factor. If they don't revel then they have to accept that we have the right to question them due to lack of confidence. It's the classic Hobson's Choice.
As for the number of collectibles of all sorts per spawn on a island i'm afraid looking at it per island is the wrong way of looking at it. A developed island or a beginner island quite simply has less area where spawns can take place. This in fact mean the system favors less developed players. In a nutshell they get more from spawns while higher players can get theirs through trading or adventuring power.