The 2011 thread on this subject also refers to overlapping tolerance of CN and C3.
This post also contains some data on tolerances from 'ten years ago'
https://www.accessnorton.com/NortonCommando/c3-vs-cn.10179/post-137420
The '2001' data are as follows:
Clearances before installation
C1 5-15microns (for a 30mm ID bearing)
C2 5-30
C0 25-50
C3 45-70
C4 60-85
C5 85-110
From the 2019 FAG HR-1 Catalogue (Section 1.10, Pg 424)
View attachment 21899
Tolerances look to have changed over time. I know it's only 2 different years, but I've attempted to show the CN and C3 differences using the ranges (max/min) plus a mid point as the mean and interpolated values using 'Box & Whisker' plots.
View attachment 21900
This shows how clearances have changed over time. There is now considerable overlap between the range of a 2019 C3 and a 2001 CN. Also increased overlap between a 2019 C3 and CN. It's therefore possible to see how a CN bearing from 2001 would fit leaving sufficient end float but also why a CN bearing to 2019 spec might not.
It's all a bit 'How many angels can dance on the head of a pin?' but at least this might help explain some of the different experiences.
Andy