Digitally signed and amended (modified) file is not shown as modified by Acrobat

My question is around metadata amendments to a digitally signed file. Basically:

1. Sign a file using Acrobat.

2. Add an amendment section changing some metadata (modified date, etc)

3. Adobe claims this file is not modified, while in fact it is.

As I understand from your digital signatures guide( https://www.adobe.com/devnet-docs/acrobatetk/tools/DigSig/Acrobat_DigitalSignatures_in_PDF .pdf )

any modification that falls outside of the /ByteRange property should flag that a signed document is modified. I am able to generate a signed file, then add metadata amendments past original %%EOF marker and Acrobat Pro DC (version 2017.012.20098) would report that the document is not modified.

My questions:

1. Why is this document not reported as modified? Is my interpretation of the guide incorrect?

2. If there are exceptions to metadata amendments on signed files, what amendments exactly are considered "harmless" and "not a modification"?

I have a minimal sample file to demonstrate this, can provide on demand

Regards,

E.H.