Is there a standard for how wildcards are dealt with in dictionaries?
The plus sign "+" is not a wildcard character. "姓氏" is.

"老" is literal in this context. "+" is a concatenation operator. "姓氏" is a variable, and is supposed to be replaced with an actual family name.  Therefor “老+姓氏” may refer to "老张", "老李", "老王", ..., but not "老blahblah姓氏"

Unfortunately not all dictionary writers learn programming, so concepts like "variables" would be foreign to them.  Even programming books in English struggle to typeset literals and variables differently.  I guess the book 《广安方言与民俗词典》 covers a much wider range of knowledge than barely syntactic patterns, thus the author may not make too much effort typesetting wildcards nicely, as long as the reader can understand what he/she means from the context.