I would argue, from a layman's perspective, that "I do not know" and "I do not remember" have significant differences, and drawing those parallels would only serve to muddy the waters. In this case it could be possible to show that the testimony was given - even if without other deceit or malice - without competence and "any reasonable person" would be aware of their lack of expertise. Just like it could be possible to show, through evidence such as correspondence, that X had knowledge of Y. I wonder if the system is resilient against such speculated abuse.

Edit: these logical inversions made my ESL head spin a bit. The point was that "I do (not) know" is more readily falsifiable than "I do (not) remember".