This just means security updates were never installed.
(Or you claim that all those operating systems never had kernel-level security issues which seems doubtful...)
Most were only locally connected (for example OS/2 had a Token Ring in one building). The WAN connection (for AS/400) was trusted.
This just means security updates were never installed.
(Or you claim that all those operating systems never had kernel-level security issues which seems doubtful...)