I am a little confused on this website. If I am using the amba4 protocol, which document should I read?

Hi,

   I am learning amba4 spec. In the URL I posted below, the spec document for the amba4 protocol is version E. However, the latest release is version K, which belongs to AMBA5 on the web page. Which document should I use as a reference?

https://www.arm.com/architecture/system-architectures/amba/amba-specifications

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