Originally Posted by 1KChinito
Theoretically, yes. In practice, three is the max assuming they are all type B vouchers. That was the max the CSR was willing and able to input.
I have a feeling OP’s $150 voucher is a type A which is considered as a discount. In that case, a type B voucher cannot be combined with a type A voucher.
Update now that I've tried this out finally: 1KChinito is, sadly, correct. The type B vouchers, which won't expire for a while, will have to wait for another trip.