Some contracts contain non disclosure agreements for a variety of reasons.Sometimes it has nothing to do with the company at all. Sometimes it's about the client's preferences or interests. This does not affect the validity of the contract.
The company has already indicated that this is the case through their previous PR's about having a legal obligation to keep certain things out of the public domain for a certain period of time.
If the basis for your wanting to sell is that you do not, as of now, know who these large accounts are, it may be worth it to wait and see.