Just also be aware they are now citing that on points plus voucher bookings, the points and voucher must come from the same account. Not sure how religiously this is enforced but I had it enforced on my booking, both when I booked originally and used one voucher to upgrade the outbound flights, and then again when the inbound flight price had dropped enough so I could use the second voucher from a different account.

If all agents are doing this it will make it quite difficult for people to use multiple vouchers. I was able to get round it on the second upgrade by gifting my voucher to my husband so then the voucher was in the same account as the original points booking. But only silver and above officially allowed to do this