We are talking about parts that were designed 40 years ago. The RCA COSMOS process was not dense enough to use MOSFETs for protection devices (couldn't fit 6 more on the chip), so they used zeners. No doubt they felt comfortable with that because of experience with their consumer bipolar ICs that had on chip zener regulators.
Also, they did not bother with "representations". If you look at die photos of old RCA parts like the 4000A series, they match the datasheet schematics.
Of course it's likely that second sources changed the protection circuits (don't they always mess with them?).
-- David DiGiacomo, San Francisco, CA snipped-for-privacy@slack.com