> ... <corr> is supposed to indicate corrections made by the
> transcriber/editor, not by the author/scribe of the copy text
> itself. Is it okay to use it for the latter - indicating the
> scribe with "resp"?

My inclination is that this (using <corr> with resp= to indicate
corrections made by the 13th century scribe as opposed to the 21st
century encoder) is not a good idea.

1) *I* think it's pretty clear that the first paragraph of 6.5.1 is
    referring to modern transcribers or encoders.

2) The words "apparently incorrect or inaccurate" also seems to imply
   a modern sensibility.

3) The fact that resp= is described (in 6.5.1) as signifying "the
   editor or transcriber responsible for suggesting the correction"
   indicated also seems to imply a modern day person.

4) The fact that the value of resp= should (ostensibly) point to a
   <respStmt> in the <teiHeader> also implies modernity, at least in
   that I've never contemplated giving 13th century scribes credit in
   a <respStmt> in the <titleStmt>, <editionStmt>, and certainly not
   in the <revisionDesc>.

However, 6.5.3 seems to deliberately leave this door open:

   where the correction is an addition by a scribe or author in a
   manuscript or other primary source (typescript, proof or galley,
   etc.) then either <corr> (or <sic>) or <add> might be appropriate,
   depending on the circumstances.                 -- P4:2002, p. 148

   where the correction is an addition by a scribe or author in a
   manuscript or other primary source (typescript, proof or galley,
   etc.) then either <corr> (or <sic>) or <add> might be appropriate,
   depending on the circumstances.                 -- P4:2002, p. 153

So I think it is up to individual projects to decide whether or not
to use <corr> in this manner. If you do, I think it is wise to
explicitly document this in the header, perhaps in
teiHeader/encodingDesc/tagsDecl/tagUsage[@gi="corr"].


> I agree that <add> should be reserved for true additions, not
> modifications

I'm not sure I understand this. I thought the Guidelines specifically
recommend <add> for modifications. See, e.g., 18.1.5 "Substitutions"
on p. 464.