“Oh my god. INN uses many non-portable data formats, which just depend on your C types.”
One server, about 200 users, nearly 30 years on 32-bit Debian, upgraded straight to 64-bit while skipping versions. The core upgrade took about an hour. The cleanup took far longer, with exim, LVM, Apache and Mailman each finding a new way to break. This is what real infrastructure looks like. It runs for decades and nobody wants to touch it.