It'd be interesting to see the trace of that session. Depending on how it used its tools, it may never have seen that comment.
This comment was there already for a very long time, so "earlier" it was OK.
And noone noticed because since these usings are unused in the code, the compiler didnt complain about missing declaraionts. (if you want to be able to debug dynamic code at runtime and changing it, requires some specific .NET packages included) - and because noone used this dynamic compilation feature for a longer time, we didnt became aware of that its missing