Missing case in rules?

Hello dear XML editors and mailing list subscribers,
I am fairly new to XML, but all my officially expert friends and acquaintances weren't able to give me a satisfying explanation about what according to my potentially wrong understanding of the specification seems like a missing case in the wording of some constraints, namely that of the well-formedness and validity constraints "Entity Declared".
I noticed that the wording for these very constraints has been changed several times over the different editions. I'm sorry to actually bring this issue up again then, but my question is: if validating processors are obligated to read and process entity declarations occuring in parameter entities or in the external subset, what happens when the document *is* standalone but names given in entity references occurring inside the external subset or a parameter entity don't match those in an entity declaration? I'd say it should be an error, but the way the two constraints are actually worded the case is left out.
My apologies if what I'm saying shows a misunderstanding of the specification on my part, in which case I ask you to kindly enlighten me on the matter.
Many thanks,
Suhel Jaber