The Statute of Limitations for copyright infringement actions is three years from accrual of the action. So, it sounds like that may pose a problem. You will need to consult a copyright litigator. if you aren't barred by the SOL, then the registrations would need to be compared for substantial similarity sufficient to make a presumption of copying. If you pass that threshold, then the damage potential would need to be assessed and forms to justify suit. I am quite skeptical that you will meet all these hurdles, but you can not handle this alone. use the find a lawyer tab and perhaps your case can be addressed. Don't expect a lawyer to call you as your identity is not known to us.
I am not your lawyer and you are not my client. Free advice here is without recourse and any reliance thereupon is at your sole risk. This is done without compensation as a free public service. I am licensed in IL, MO, TX and I am a Reg. Pat. Atty. so advice in any other jurisdiction is strictly general advice and should be confirmed with an attorney licensed in that jurisdiction.
I understand that your major concern is that proper credit be applied to your husband and this may affect your strategy. Unfortunately, the US Copyright law doesn't recognize a sting moral right, so your complaint would be civil and monetarily based. But it is common to begin disputes over copyright infringement with a cease and desist letter drafted by an attorney to the artist in an attempt to spark negotiations. Here you may only be looking for enough money to cover your legal fees required to get the other artist to sign an agreement recognizing your husband's authorship.
The above response is general information ONLY and is not legal advice, does not form an attorney-client relationship, and should NOT be relied upon to take or refrain from taking any action. I am not your attorney. You should seek the advice of competent counsel before taking any action related to your inquiry. less