The short explanation
The base block is 128 bytes: manufacturer, basic timings, the preferred timing. Everything modern — HDR support, audio formats, high-bandwidth video, Dolby Vision — lives in extension blocks stacked after it.
Two blocks makes 256 bytes, the familiar size. Modern displays need more: 384 bytes (three blocks) or 512 (four).
Where you run into it
A device that reads only the first two blocks silently truncates the rest. Everything declared in blocks three and four never reaches the source — and there is no error, just a capability that quietly does not exist any more.
That is the single most common way an 8K display ends up being treated as a 4K one.
How the DR HDMI 8K handles it
DR HDMI 8K firmware 1.3 added 384 and 512-byte EDID support in copy-TX-sink mode, 1.4 extended it to the custom slots and AutoMix, and 1.5 fixed two-block reading of the sink. You can download the raw EDID from either side and inspect it, and the complete hexadecimal blocks appear in the exported configuration file.
Want to test your own HDMI chain?
The DR HDMI 8K is sold through the HDFury.eu web shop.