What this indicates is that the TK designation doesn’t necessarily refer to Stormtroopers in particular, but a specific unit of the Imperial military. In the canon anthology book From a Certain Point of View, the Stormtroopers who serve on the Death Star and board the Tantive IV are referred to by TK numbers. The TK in their operating numbers likely designates one of the units under the command of Darth Vader and Grand Moff Tarkin. Similarly, every Stormtrooper who appears in the Legends novel Rebel Force: Hostage uses an operating number that begins with “TB,” indicating their shared division.
Valin Hess asking for a TK number instead of an operating number makes sense since Djarin and Mayfeld were disguised as Juggernaut Pilots under his command. It can be assumed that all troopers in the Morak Imperial remnant are part of a larger legion referred to by TK operating numbers. Given that Imperial forces with TK numbers have been seen at the Battle of Scarif, capturing Princess Leia, patrolling the first Death Star, and, as revealed in The Mandalorian season 2, participating in Operation Cinder, the larger unit it refers to has a storied history in the Star Wars franchise.