Originally Posted by Steve in Olympia

Not quite. The first line I quoted refers to redeeming the voucher, not the initial earning of the voucher:
"The Redemption Voucher allows the main BA/Chase account holder, when making a return flight booking using BA Miles, to book another seat on the exact same journey ..."

The second line I quoted refers to the time of actual travel, not earning the certificate:

"Members must remain eligible for this promotion at the time of travel."

Both quotes refer to using the certificate, not earning it. Neither sentence refers to earning the certificate. Yes, that is a big difference.

Folks are free to cancel their cards, based on the advice on this forum. My only point is that the Terms & Conditions are not back-and-white on this point, and the risks are not insignificant.