6.6L Duramax L5P how much does model year matter when choosing aftermarket parts?

I've been looking into the 6.6L Duramax L5P used in Silverado and Sierra HD trucks, and one thing that keeps coming up is how misleading a simple “fits L5P” description can be.

Even within the L5P generation, some components seem to have fairly specific year breaks. For example, the CAN-bus side isn't identical between the earlier 2017–2019 trucks and later models, while exhaust, downpipe and crankcase-ventilation hardware can have their own fitment ranges.
For anyone here who has worked on multiple L5P model years, what information would you verify before buying aftermarket hardware?
I'm mainly trying to understand the differences around:
Silverado/Sierra 2500HD vs 3500HD
2017–2019 vs later L5P trucks
CAN-bus and emissions-module connections
Downpipe and exhaust routing
CCV/crankcase-ventilation hardware
Pickup vs cab-and-chassis fitment
EGR-side hardware
It seems safer to identify the exact truck, year and configuration first rather than assuming that every part marketed for a 6.6L L5P is interchangeable.
I'd be interested to hear from anyone who has actually worked on both the early and later L5P platforms.