Recent discussions on Council and TEI-L suggest that there are two distinct views on how @corresp should be used.
Lou's strong view is that @corresp "really is meant only for cases where the target and the source are interchangeable, as for example where one translates the other. I also think it is meant to be bidirectional -- that is, if corresp(a.b), then corresp(b,a)."
The other view (held by me, and I think also by James) is that it's a general-purpose attribute for linking between two things that have virtually any relationship the encoder wishes to capture. The definition of the attribute would seem to support this lax view: "points to elements that correspond to the current element in some way".
I think we definitely need to clarify this, since the lax use of @corresp is widespread. If indeed Lou is right, and @corresp is a specialist attribute, then I think there is a clear and desperate need for a general-purpose global linking attribute -- @link, perhaps. There are many use-cases, but here is one:
In a personography representing the characters appearing in a Shakespeare play, an individual character may have different names in different versions. I need to specify, for each <persName> element inside <person>, which versions of the work it is used in. So using @corresp, I would do this:
<persName corresp="ver:F1 ver:FM ver:Q2 ver:Q2M ver:EM">Polonius</persName>
<persName corresp="ver:Q1 ver:Q1M">Corambis</persName>
Other characters may only appear in some versions of the work, so the same attribute needs to be available on <person>.