some malfunction in systems around the world only supporting max 9 digits
That’s not how computers work, though. They use binary so they care more about binary digits (powers of two: 1, 2, 4, 8, 16, 32, etc) rather than decimal digits (powers of 10: 1, 10, 100, 1000, 10000, etc).
Very old systems store numbers with a fixed number of digits, but those systems don’t use Unix time.
That’s not how computers work, though. They use binary so they care more about binary digits (powers of two: 1, 2, 4, 8, 16, 32, etc) rather than decimal digits (powers of 10: 1, 10, 100, 1000, 10000, etc).
Very old systems store numbers with a fixed number of digits, but those systems don’t use Unix time.