monte carlo OAS if the prepayments are path-dependent (e.g. fixed-rate mortgage) binomial OAS if the prepayments are not path-dependent (e.g. callable corporate bond) the auto loan was Z-spread because it made it pretty clear that there were virtually no prepayments.
How is defeasance call protection? it doesnt stop prepayments at all from coming in. It just takes the money and puts it into treasuries… So it really wasnt preventing any kind of prepayment… My understanding is wrong i am sure… another -1… got the z spread one tho