In most aspects, Stargirl has been an accurate adaptation of the comics, but one element of her story – where the Comic Staff fits into the Justice Society mythos – actually borrows more from Smallville than it does the comics.
Brec Bassinger’s Stargirl is the third live-action take on the DC Comics heroine. Like the first two, Stargirl’s Courtney Whitmore is tied to the Justice Society of America and a powerful weapon known as the Cosmic Staff. Preceding Bassinger was Sarah Grey, who played the Arrowverse’s Stargirl in Legends of Tomorrow season 2. This version was part of the original JSA, as opposed to a legacy hero. The very first version, portrayed by Britt Irvin, made her debut in a two-hour, Justice Society-themed Smallville movie event titled “Absolute Justice.” She was introduced as a hero who took up the Stargirl mantle and Cosmic Staff after the death of her mentor, Sylvester Pemberton, aka The Star-Spangled Kid.
That’s a bit different to Stargirl’s interpretation, which saw Pemberton's Starman (Joel McHale) supposedly die before even meeting Stargirl, who mistakenly thought he was her father when she started using his Cosmic Staff. However, it’s worth noting that Smallville and Stargirl do share an interesting connection: in both versions of the story, the Cosmic Staff was previously wielded by Sylvester Pemberton, a famous hero whom Courtney idolized. That’s different to Stargirl’s comic origin, which established that she acquired Pemberton’s Cosmic Belt and outfit, but not the staff. That, she acquired after becoming a superhero. In DC Comics, the Cosmic Staff was not one of Pemberton’s possessions. Instead, it had belonged both to Ted Knight’s Starman and his successor, Jack Knight.
It was really Smallville that essentially made Sylvester Pemberton into Starman first by giving him the Cosmic Staff. Stargirl double-downed on this change by officially giving him the “Starman” mantle, in addition to the staff. Stargirl copying Smallville’s use of Pemberton rather than go with the comics makes sense, especially when looking at the source of all these stories Smallville’s “Absolute Justice” special, the Stargirl comic series, and the Stargirl TV show were all crafted from the mind of Geoff Johns. What that means is that when adapting Smallville’s Cosmic Staff change, Johns was basically just revisiting ideas he originally developed.
Plus, Stargirl moving in this direction works better for the series, as it allows it to focus on Courtney’s efforts to follow the footsteps of just one superhero. Stargirl getting Pemberton’s equipment and becoming the new Star-Spangled Kid, and then evolving into Stargirl when she found Jack Knight’s staff may have worked for the comics, but the situation was different for the show. It was necessary for the overarching plot of the series for Courtney to obtain the Cosmic Staff right away. Throwing Jack or Ted Knight into the mix (with Pemberton) that early in her story would only have complicated things. The best way to fix that was to merge Starman with the Star-Spangled Kid, and that’s ultimately what Stargirl – and Smallville – did.