THe first mistake is that by testing every assumption through his questions he is bringing the attention to the jury that the determination of the dates is complex and the jury may ask itself whether any witness could be relied on.
The second mistake is one of strategy. When the real bug guy testifies he will know exactly how Feldman is going to cross so he will be better prepared. Goff won't make the same mistakes.
Goff will not make the same mistake as this guy. Goff will not try to B.S. his way past Feldman and will simply answer the questions asked by Feldman without trying to spin like this guy is.
Are you suggesting that you will believe the third bug guy but not the one hired by the prosecution or the one that backed him up?