I had a shocking surprise when I bocked my first fligth involving different unused ST carriers (each one with its own code) and different zones* and stop overs.

*With different zones I mean zones where there's a specific baggage allowance.

Quite cerebral and I haev difficulties to explain, an example can explain better.
All in the hightest class (First for AF, Biz/First for CO, Biz for KLM and NW, Economy for AZ domestic)

Unique ticket:
HOU-CDG (AF) connecting with CDG-VCE (AF)
stop over
VCE-FCO (AZ)
stop over
FCO-AMS (KL) connecting with AMS-NRT (KL)
stop over
NRT-HNL (NW)
stop over
HNL-HOU (CO)

Max allowance
2 pieces of 32 kg each for USA-EU for AF
20 kg for a domestic fligth in Italy
30 kg for EU-Japan with KLM
2 pieces of 32 kg each plus an extra one of 18 kg for Japan-USA with NW
3 pieces of 32 kg with CO

So, to avoid paing any penality, you need to have only 20 Kg. The lowest limit. Each of the mentioend carriers has no visibility it's part of a more complex routing with different baggae allowance.
Remove the stop over in Rome (FCO), so you remove the 20 kg bottleneck with a VCE-AMS with KLM and you are limited by KLM with 30 Kg. If you are in connection, like CDG-VCE, you avoid the problem but it's not a viable answer.