All the options could be said by native speakers, but all are not equally good. Also, some carry different nuances or are associated with different pragmatics.
(A) He talked about validation of the new product.
(B) He talked about the validation of the new product.
Sentence 1(A) has a generic reference to "validation" and is substantially equivalent to saying: "He talked about validating the new product." Such a generic usage is best when product validation is not a concept already prominent in the shared discussion background of the people talking. In other words, it does not reactivate an existing entity in the shared atmosphere of the discussion. It is also good to describe something that is not yet detailed enough in their common frame of reference to merit a specific reference.
Sentence 1(B) instructs the listener to reactivate some specific instance of validation that both parties would be familiar with. It conjures up an idea of existing documentation that represents the actual validation. Before validation actually happens, the "instance of validation" remains somewhat vague, especially if unconnected with more specifics, such as a date, specific documentation, a specific result, or specific date. Before the event of validation, it is probably more common to use a generic reference and omit the article, since the specific instance is still too uncertain.
These distinctions would also apply if you replaced "validation" with "design," "manufacture," "marketing," etc.
(A) The new feature can make control of the system more difficult.
(B) The new feature can make the control of the system more difficult.
Sentence 2(A) is a generic reference to control and so applies to any instance where control might be difficult. You could replace it with "The new feature can make the controlling the system more difficult."
Sentence 2(B) feels slightly strange because it suggests that "the control" is a specific entity already known to the parties and distinct from other instances of control. In a highly technical discussion, where the manner of system control is highly differentiated from control of other systems, this usage becomes better; however, even then a generic reference to control would always be possible.
Why is "control" different from "validation," "design," "manufacture," and "marketing"? I think it is because in a company the latter can be associated with specific documentation, procedures, and protocols central to company operations. They have things about them that can differentiate one instance from another. "Control" is just a generic aspect of every system on the planet and usually doesn't have further specifics associated with it in people's minds.