In Posey v. Med. Center-West, 257 Ga. 55, 59 (354 S.E.2d 417) (1987), the Supreme Court eliminated the longstanding rule that the release of one joint tortfeasor releases them all. As the Court stated: "A valid release of one tortfeasor from liability for a harm, given by an injured person, does not discharge others for the same harm, unless it is agreed that it will discharge them." Posey, 257 Ga. at 59. The effect of the holding was to limit the effect of releases to those the parties intended to release. The Court went on to hold that parol evidence was allowed to show exactly whom the parties intended to release. Again, in the words of the Supreme Court: "We further add that the intent of the parties to the release regarding its effect may be proven by external evidence as against a third party. One not a party to the release may not object to the external evidence under the parol evidence rule." Posey, 257 Ga. at 59. The effect of this language allowed introduction of parol evidence against both named and unnamed nonparties to show whether they were covered by the release.