Going back to first principles
If the index includes only the burial place -- even though the register includes an exact flipping address for the death -- Source Linker high-handedly decides that you don't have a death place, you can only add or edit the death date.
If the index labels it a marriage registration, Source Linker Knows Better Than Thou and will not let you create a marriage event.
If it's entered as a christening, Source Linker doesn't show it at all unless you're attaching something that's also labeled exactly and precisely as a christening.
If the index only includes the christening date, then you can't tag the birth in Source Linker, no matter how precisely the birthdate and time are also given in the actual document.
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Why does Source Linker worship the index like this, as if it were some sort of deity? And why does Linker get to make these decisions for us, when it clearly doesn't know better?
Instead of creating fancy algorithms for deciding whether a conclusion is different from the indexed value, just decide whether the tree side can be edited directly from Source Linker or not. My vote is for "not", unless Linker is changed fairly drastically, to show everything that's already there, not just the select tidbits that satisfy its literalist criteria.
The index should not be king. It should just be a finding aid, and what Source Linker should be attaching is a reference to the actual record.