Follow up tweet from Sawyer:
"Bruno says they've already successfully tested 12 engines in addition to the two used during the flight readiness firing, adding it's not the first engine to do that and won't be the last, noting it's happened on other ULA-used engines. "It's not a news story""
Some insight in to the # of engines they have...
That is good news. I love SpaceX and root for everything they do but having a decent back up for critical launches is good thing.