Fender Rumble 25 PR499

Looking at similar Fender amps, I only have the one Rumble 25 drawing, but the guitar version - Frontman 25 - includes several revisions. The revision A uses the TDA 1514, while the revision B board uses the LM3876.

This sort of thing was common. Companies like Fender would change a circuit to adapt to changing supplier situations. The National chip might have been easier to keep production quantities coming compared to the TDA chip.

Either IC is "correct", it just depends on which board your amp used.