The case of Neiman-Marcus v. Lait, 13 F.R.D. 311 (S.D.N.Y. 1952), provides a good illustration of this general rule. In that case, the defendants wrote that "most of the [Neiman-Marcus] sales staff are fairies" and that some of the company's saleswomen were "call girls." Fifteen of the 25 salesmen and 30 of the 382 saleswomen at the store brought suit for defamation. Applying New York and Texas law, the court held that the salesmen had a valid cause of action, but the saleswomen did not. Even though the statement referred to "most of" the salesmen, without naming names or specifying further, the statement could be understood to refer to any individual member of this small group. The group of saleswomen, however, was so large that a statement that some of them were "call girls" would not be understood as referring to any individual member of the group.
As to the second exception to the rule against group libel -- when circumstances point to a particular individual -- courts have allowed defamation claims where the statement is facially broad, but the context makes it clear that it referred to the plaintiff. For example, Bill Blogger may be able to claim defamation based on the statement "all bloggers who attended the most recent city council meeting payed bribes to the mayor," where Bill is the only blogger who attended the meeting and readers will therefore understand the statement as being a thinly veiled indictment of him.
A company or organization can be a defamation plaintiff. In fact, the largest jury verdict every awarded in a libel case came in a case brought by a business plaintiff.
Note that each state decides what is required to establish defamation, so you should review your state's specific law in the State Law: Defamation section of this guide for more information.