Before Stephen Sondheim left us at the age of 91 last November, he had long since been anointed as the reigning super genius of the modern musical theater. I have seen roughly 10 Sondheim tribute shows or concerts for every one saluting Cy Coleman or Jerry Herman, two of his contemporaries whom I would argue are worthy of the same degree of attention. Yet while other Broadway giants deserve a little more love, I would never claim that Sondheim should receive any less.  

From the beginning, alongside his official canon of 19 mostly classic musical shows, there has been a side Sondheim industry that includes alternate lyrics, tunes, and assorted bric-a-brac. In science fiction terms, we would call this “the extended universe.”

Two of the shows at Feinstein’s 54 Below this month are by official Sondheim original cast members, Donna McKechnie (“Company”) and Liz Callaway (“Merrily We Roll Along”). Last weekend at the 92nd Street Y, a pianist, arranger, and conductor who worked with the composer on numerous occasions, Ted Sperling, put together his own retrospective of the maestro’s love songs. 

“Isn’t It Bliss? Sondheim on Love” featured two female and two male singers, a format we remember from the 1999 revue “Putting It Together.” There’s an appreciable age difference between the older baritone (Ben Davis, with gray beard) and the younger one (Jordan Donica, with man bun), though no obvious such difference in the two sopranos, Solea Pfeiffer and Scarlett Strallen.  

Interspersed with personal reminiscences from Mr. Sperling, “Isn’t it Bliss?” was indeed blissfully arranged for the four voices plus string quartet and rhythm section, and also exquisitely sung. There’s nothing wrong with a “greatest hits” show like this, especially when they throw in some rarities, like, “I Wouldn’t Change a Thing” (from “The Last Resorts”) and “The Girls of Summer,” worthy ephemera I’ve never heard anywhere else.  

Otherwise, it’s a well-assembled retrospective of songs and scenes that doesn’t change much. “By the Sea” is still sung with a cockney accent — I think I like it even better here, without all the murdering, than in “Sweeney Todd” — and “Barcelona” (“Company”) is still a tender waltz, though I wish just for once “Bobby” wouldn’t moan “Oh God” at the end. (I keep thinking if I were him, I’d be ecstatic that April wanted to stay with me rather than schlep to Barcelona.) All four singers were impressive, especially Mr. Donica: I enjoyed his performance so much that I was willing to forgive him his man bun.

The other Sondheim show in Manhattan in the last few days was Jeff Harnar’s “I Know Things Now,” which is also a new CD from PS Classics; both the show at the Laurie Beechman and the album (which features a 21-piece orchestra with strings) are arranged and conducted by Jon Weber. Mr. Harnar has subtitled the show, “My Life in Sondheim’s Words,” and he is to be commended for letting the songs tell his story.

The aim is to reconsider and recontextualize the Sondheim catalog.  Mr. Harnar starts with the subtle but radical move of making “I Know Things Now” (“Into The Woods”) work in entirely different ways merely by singing it to a swinging 4/4 jazz beat. It’s simple but effective. Then there’s “Buddy’s Blues,” written in the general spirit of “Follies” as an old-time vaudeville number; Mr. Harnar treats it as something more like a Harold Arlen blues, a true saloon song, with occasional nods to Jimmy Durante.

He delivers “The Ballad of Sweeney Todd” as a fast modal jazz number, inspired directly by Lea Delaria’s now-iconic arrangement.  The masterpiece may be a collage of tunes centered around “Getting Married Today.” As originally written for “Company,” the number is already a medley unto itself, in which the composer switches between three separate sets of word and music. Mr. Harnar had the ingenious idea of taking one of those tunes and switching these other songs in and out of the number: “The Little Things You Do Together,” “Marry Me a Little” (both “Company”) and “I’m Calm” (“Forum”). More than a conventional medley, it feels like D.W. Griffith cross-cutting between thrilling scenes at the climax of “Intolerance.”

These are two singularly special presentations, but more (much more) Sondheim is on the way. Here’s an idea: Let’s license the name and start a cabaret room called “Sondheim’s.” He’s already got a theater named after him, so why not a nightclub? Anybody want to invest? Oh, the line forms to the right, Babe.