Few operas are perfect, but Puccini’s first and last operas have shortcomings that are hard to overlook.They also have strengths, which is why the Collegiate Chorale presented the early “Le Villi” and the final, unfinished act of “Turandot” at Carnegie Hall on Monday evening. Juxtaposing the two gave an arresting glimpse of Puccini’s stylistic progression in his wildly successful career.

Of the two offerings, the act from “Turandot,” though more familiar, was the more newsworthy, as it included the New York premiere of the ending composed by Luciano Berio and first heard in 2003 (the year before Berio’s death). In considering the thorny issues surrounding “Turandot,” one must always bear in mind that Puccini didn’t just happen to die before he could finish the opera. He struggled on and off for several years to solve an artistic problem: how to make the icy heroine from Gozzi’s fairy tale of antique China appear sympathetic at the final curtain, when she is responsible for the torture and death of the opera’s sympathetic character, the slave girl Liu?

The challenge may well be insurmountable, but in composing the ending that became standard soon after the opera’s posthumous premiere, the composer Franco Alfano seemingly held his nose, wrote a passionate duet for Turandot and her successful suitor, Calaf, and sealed the “happy ending” with a garish choral reprise of the tune from “Nessun dorma.”

Berio’s solution, based on a more thorough study of Puccini’s sketches for the final scene – of which there are many – is more interesting for several reasons. First, his music gives Puccini’s familiar melodies a refreshingly modernistic update, but not obtrusively so. Second, the Berio ending picks up on a reference by Puccini to “Tristan,” and includes a long, Wagner-like orchestral interlude representing Turandot’s transformation into a creature capable of love. Finally, Berio ends the opera on an ambiguous note after Turandot identifies Calaf’s name as “Love,” instead of hammering home the close. I would vote for the Berio ending becoming standard, although royalties are said to be prohibitively expensive.

The word “Amor” at the close took Aprile Millo into her recalcitrant upper register, but the veteran soprano still exudes a Tebaldi-like glow in other parts of her vocal range and brings a diva’s phrasing to every line. It was a pity she stood behind a music stand, reading the score with glasses – Hei-Kyung Hong was much more effective for having Liu’s music memorized. Ms. Hong also sang beautifully, showing an irresistible mix of resolve and vulnerability in her torment. Franco Farina mustered the vocal wherewithal for a lusty “Nessun dorma,” even if the voice didn’t always sound steady or cleanly produced. Lester Lynch was strong as Ping.

“Le Villi” began as a competition entry for which Puccini, then in his mid-20s, failed to win even an honorable mention. But the composer’s supporters managed to have the opera produced in Milan in 1884, and, even more important, it won Puccini the admiration of the powerful publisher Giulio Ricordi.

Ferdinando Fontana’s libretto tells the simple story of the young couple Roberto and Anna. To her distress, he must leave on business, but assures her of his eternal faithfulness. In fact, he gets mixed up with a siren, and Anna dies of a broken heart. But her ghost returns and with le villi (fairies) dances with Roberto until he dies.

The fine opening scene celebrating the couple’s engagement – which features handsome contributions from the chorus, including a charming waltz – could set the stage for a longer opera than this one-act work (which Puccini later stretched to two acts).But it is oddly constructed, and Puccini relies on two poems, recited appealingly by Antoinette LaVecchia on Monday night, to narrate important action. The ending makes surprisingly little impact.

“Le Villi” is said to be influenced by other composers – Verdi, Catalani, Ponchielli – and, as a youthful work, this is expected. But “Le Villi” also sounds like Puccini. And it has a freshness that the later, more conniving master of theater sometimes obscures (think of all the Orientalisms glommed onto “Turandot”).

Ms. Millo had a fine go at the opening cavatina in which Anna, with remarkable presence, repeatedly urges Roberto not to forget her, and later Mr. Farina expressed guilt wrenchingly in Roberto’s aria of remorse. As Anna’s father, Guglielmo, Carlo Guelfi was alert to words but sang rather drably. The chorus excelled in the big prayer ensemble “Angiol di Dio,” a fine piece that calls to mind (but predates) a similar number in “Cavalleria Rusticana.”

You wouldn’t necessarily think that opera in concert is the mission of a choral ensemble, but the excellent Collegiate Chorale has been putting on important opera performances for so long that it is now an important part of New York’s musical life.The Orchestra of St. Luke’s makes a fine contribution, too. And the conductor, Robert Bass, clearly responds to this repertoire. Otherwise, he wouldn’t be doing it.