I honestly think it should be disclosed. Having jubilee in the mix will create red leakage in mottled birds. Maybe not all of them, but I would think a good percentage of them. I think a lot of people did this to churn out mottled chicks faster. I may be wrong though. Hopefully the seller disclosed it to you.
I am going to agree with you, there are a bunch of auctions on rarebreed and they are either for chicks of both patterns from the same parents, or the parents and its stated that they produced Jubilee. I was told NOT to breed Jubilee into the spangled, and not to breed two spangled x jubilee together, or you would continue to get jubilee and lots of leakage issues in the spangled.