Many courts extend opinion work product protection to a lawyer's selection of intrinsically unprotected documents used to prepare a deponent, the identity of witnesses important enough to interview, etc. This approach is frequently called the Sporck doctrine, after a Third Circuit case. Sporck v. Peil, 759 F.2d 312, 315 (3d Cir. 1985).

In McClurg v. Mallinckrodt, Inc., No. 4:12-CV-00361-AGF, 2016 U.S. Dist. LEXIS 29230 (E.D. Mo. Mar. 8, 2016), defendants' lawyers collected documents from Missouri's Historical Society and from the government through FOIA requests. Plaintiff filed discovery requests seeking the identity of those documents. The court concluded that the documents defendants had obtained from the Historical Society were not responsive. After reminding defendants that they must produce all responsive documents they had obtained from any source, the court also denied plaintiffs' request to identify the specific documents defendant had obtained through FOIA — concluding that forcing defendants to re-produce those documents as a "supplemental production" would "reveal their opinion work product." Id. at *12.

Lawyers should keep in mind that their selection of even intrinsically unprotected documents can reflect their opinion, thus justifying withholding those documents' identity. However the Sporck doctrine only protects the documents' identity — and applies only if the adversary also has the documents themselves.