This was almost 30 years ago so my memory is fading, but pre-devfs when they were just in the /proc tree you could tell the kernel to bring them up in a given order and so assign the name you wanted to a given card.
Network interfaces always had names sequentially assigned by the kernel. systemd overrides them based on PCIe bus location, which changes when you install new hardware. Lennart insists that PCIe bus locations don't change when you install hardware, even though this is obviously wrong as proven by real–world evidence.