I'd be inclined to be honest and say, @at the time of the analysis the chosen programme was the most suitable I knew of' and look into the newly found one as would have done differently. Saying that, I'm taking the honest approach as I consider blagging a risk. What if they KNOW it's not? You know it's not so your defense may not be as strong either as you won't believe in it! Is the one you used the second best?