Textual errors? That's unfortunate, considering the efforts made to avoid them. Here are the sources. Additional corrections were supplied by S.T. Joshi.
21 of the stories come from:
The Dunwich Horror and Others, S.T. Joshie, ed. (Sauk City, Wisconsin: Arkham House, 1984.) Corrected eleventh printing.
At the Mountains of Madness and Other Novels, S.T. Joshi, ed. (Sauk City, Wisconsin: Arkham House, 1985.) Corrected ninth printing.
Dagon and Other Macabre Tales, S.T. Joshi, ed. (Sauk City, Wisconsin: Arkham House, 1986.) Corrected ninth printing.
"The Shadow Out of Time" is reprinted from
The Shadow Out of Time, S.T. Joshi and David E. Schultz, ed. (New York: Hippocampus Press, 2003.)
21 of the stories come from:
The Dunwich Horror and Others, S.T. Joshie, ed. (Sauk City, Wisconsin: Arkham House, 1984.) Corrected eleventh printing.
At the Mountains of Madness and Other Novels, S.T. Joshi, ed. (Sauk City, Wisconsin: Arkham House, 1985.) Corrected ninth printing.
Dagon and Other Macabre Tales, S.T. Joshi, ed. (Sauk City, Wisconsin: Arkham House, 1986.) Corrected ninth printing.
"The Shadow Out of Time" is reprinted from
The Shadow Out of Time, S.T. Joshi and David E. Schultz, ed. (New York: Hippocampus Press, 2003.)