This holds true for forms, drills, partner exercises or whatever. It would be refreshingly honest.
Many teachers pass down a lineage or a tradition from a long line of their predecessors.
When they add or modify what they were taught, they are breaking that tradition and they are fooling their disciples. If you don't care about lineage, it's not a big deal. But if you're a traditional martial artist, it's a very big deal. Loyal students are sometimes tricked by the lies and non-disclosure of the truth by their sifu. They will fight to the end to defend their sifu's honor, even when they are wrong.