If you want to use this work commercially, you should seek advise of a licensed lawyer.
If you are just asking out of curiousity, then
17 U.S. Code § 405. Notice of copyright: Omission of notice on certain copies and phonorecords:
(a) Effect of Omission on Copyright.—With respect to copies and phonorecords publicly distributed by authority of the copyright owner before the effective date of the Berne Convention Implementation Act of 1988, the omission of the copyright notice described in sections 401 through 403 from copies or phonorecords publicly distributed by authority of the copyright owner does not invalidate the copyright in a work if—
- the notice has been omitted from no more than a relatively small number of copies or phonorecords distributed to the public; or
- registration for the work has been made before or is made within five years after the publication without notice, and a reasonable effort is made to add notice to all copies or phonorecords that are distributed to the public in the United States after the omission has been discovered; or
- the notice has been omitted in violation of an express requirement in writing that, as a condition of the copyright owner’s authorization of the public distribution of copies or phonorecords, they bear the prescribed notice.
So if a few samples have been released without a copyright notice, that doesn't change anything. If the copies have been made generally available without a copyright notice, this would seem to indicate that the recipients of those copies can assume that no rights are reserved until further notice. "Until further notice" because of part (b):
(b) Effect of Omission on Innocent Infringers.—
Any person who innocently infringes a copyright, in reliance upon an authorized copy or phonorecord from which the copyright notice has been omitted and which was publicly distributed by authority of the copyright owner before the effective date of the Berne Convention Implementation Act of 1988, incurs no liability for actual or statutory damages under section 504 for any infringing acts committed before receiving actual notice that registration for the work has been made under section 408, if such person proves that he or she was misled by the omission of notice. In a suit for infringement in such a case the court may allow or disallow recovery of any of the infringer’s profits attributable to the infringement, and may enjoin the continuation of the infringing undertaking or may require, as a condition for permitting the continuation of the infringing undertaking, that the infringer pay the copyright owner a reasonable license fee in an amount and on terms fixed by the court.
Which is to say, that if someone does establish ownership of this IP in the future, even if the past infringers may be compelled to pay unpaid licensing fees, no punitive action can be taken against them for their actions taken before they have received the notice of copyright registration.