Just to close the loop on this, I noticed today that a $600+ trip credit that I had was not showing up in my account. I called in and the agent said that as part of the security procedures when they lock your account, they invalidate the trip credit and when you want to use it you have to call in and they will ask security questions and re-validate it. So my credit is still there but it does not show up in my account.

So just a PSA; if your account was locked and you are not sure if you had credits, you may want to look through your old email (searching for "trip credit" worked well for me) and see if you had any unused ones. You will need the number from the email (it looks like a ticket number but the first few digits after the "001" are apparently different for tickets vs other documents) when you call in. And of course the expiration date remains the same. The only real downside is that since it doesn't show up in your account it may be easier to forget about it.