I love geeking out about little details like this, so here's the scoop from my point of view. Haganezuka forged three separate swords for Tanjiro over the course of the story. The first one is the familiar black-bladed Nichirin that Tanjiro carries early on, and after it became damaged in heavy battles, Haganezuka — being the stubborn, prideful smith he is — ended up making replacement blades. By the time we get to the 'Swordsmith Village' part of 'Demon Slayer', it’s clear Tanjiro has been through multiple blades, and Haganezuka has crafted a total of three for him.
I always picture Haganezuka grumbling while pounding metal, muttering about chips and cracks, yet secretly being thrilled to make another for Tanjiro. Those three swords show the toll of Tanjiro’s fights and the bond (weird and loud as it is) between warrior and smith. It’s a small detail that says a lot about how exhausting demon hunting is, and how the people behind the scenes — like Haganezuka — quietly shape the hero's journey. I kind of love that sentimental, scratched-up lineage of blades; it feels lived-in and real.