Migrate an AIR application to use a new certificate

I'm attempting to migrate an AIR application developed many years ago to a new certificate because the old one expired. I'm using the command line tool adt version 3.5.0.6.00. To do this, I'm attempting to use the instructions from here:

Adobe AIR * Signing an updated version of an AIR application

These are the basics steps described on the above page:

To migrate an AIR application to a new certificate while updating the application:

1. Create an update to your application
2. Package and sign the update AIR file with the new certificate
3. Sign the AIR file again with the original certificate using the -migrate command

An AIR file signed with the -migrate command can also be used to install a new version of the application, in addition to being used to update any previous version signed with the old certificate.

I'm able to successfully complete steps 1 and 2 (creating/signing a new version of the AIR application with a new certificate). However, when I attempt to complete step 3 (sign the AIR file again with the original certificate), I receive the error that the "certificate has expired". This is of course accurate (hence me attempting to "migrate"). My understanding is that my original certificate expired on 10/31/2017, but I'm unsure of how to verify this information.

Anyone have any ideas of how to resolve this?

Thanks,

Patrick