I could understand that approach, however what Mueller has said about their lies up to this point doesn't seem to be making two different statements when asked the same question. Most of the statements were denials about foreign contacts which the special counsel seems confident they are lying about. It seems more like a case of getting caught red-handed and that is why they plead guilty.
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Here's an article that has a rundown of the lies Mueller believes some of the main players made: https://www.washingtonpost.com/politics/2019/01/28/lies-alleged-lies-trump-team-has-told-mueller-probe-dissected/?utm_term=.1d2d3c22b49d