NTPv4 128-bit date format:

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RFC 5905 section 6 needs to be read carefully. It's about NTP data types. It states:

• "Eras cannot be produced by NTP directly, nor is there need to do so. When necessary, they can be derived from external means, such as the filesystem or dedicated hardware."

• "The 64-bit timestamp format is used in packet headers and other places with limited word size."

This illustrates that the 128 bit date format is (possibly) used internally in the NTP nodes only, and not represented in the packet format.