Link ports on different SGB models?

On "Separating between SGB and SGB2":

> Reportedly, some SGB models include link ports (just like handheld gameboy) (my own SGB does not have such an port), possibly this feature is available in SGB2-type models only ???

Start by reviewing the project's existing Game Boy reference material around the quoted distinction between SGB and SGB2, then verify the hardware claims for each model. Done means documenting a sourced, unambiguous answer about which SGB models include link ports and updating the relevant reference section.

Written by the indexing model from the issue text.