Hi Oliver,
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The reference in the text appears without any flaw and the list contains an empty entry! The external bib file doesn't even exist. Now delete the ams option and at least the bogus list entry will disappear. However, in the text no trace of any error whatsoever.
That is the chicken and egg problem I was talking about. When the publication list sort order is 'by citation order', and 'only show cited publications' (as per ams), then \cite looks at the list to find the number, and the list checks the \cite order for what to include. All is good if the ref is actually there, but intercepting errors is problematic.
Wouldn't it be nice to just replace the "(Xxxx, 0000)" entry by "??" to make it consistent with the cross referencing errors?
I did it this way, because I prefer better-matching page breaks over visual similarity. At least some of the other \cite options generate ?? instead. Best, Taco