Are stealth companies in an industry sector?
Answer: My assumption is that the VC knows what industry and sector the stealth company is in, or they wouldn't have invested in the company. However, if you assumed otherwise in your design, it is OK.
How can a relation that doesn't have two tuples that agree in A satisfy a
FD like A->B?
Answer: Remember that an if-then statement is always true when the hypothesis is false. A FD is a statement of that form: ``if t1[A] = t2[A] then t1[B] = t2[B],'' for example. If there are no two distinct tuples that can play the role of t1 and t2, then t1 and t2 must be the same in the quoted statement. Thus, the conclusion of that statement will surely be true, and the FD is satisfied.