Interesting questsion, Joe, about whether Ira Gershwin wrote any lyrics for Porgy and Bess. I know that George sought out author DeBose Hayward (I'm not sure of the exact spelling, either) to write the "libretto" for his "folk opera," but that may have included only the script ~ the spoken dialogue ~ which of course didn't have to rhyme, although it DID have to portray the early-20th-century African-American spoken language of South Carolina with a fair degree of accuracy.

The author was presumably better able to write acceptably authentic dialogue than either Gershwin brother, but was probably not nearly as well-qualified as Ira to write song lyrics in that terribly clever rhyming style so nicely described in that Guardian article.

The sublime "I've Got You Under My Skin," by the way, is the work of the masterful Cole Porter, one of the very few lyricists who might be considered even better than Ira as an exemplar of that genre.