As you have found, parsing natural language is not an easy task! People have tried to create grammars for natural language; they start out simple, but all thecombinatorial possibilities and special case results in a mess of rules that are difficult to make sense of.

It seems to me that without a consistent structure, a hierarchical grammar will not really help you. But you can loosen the rules of a grammar to accept more possibilities. For instance,

showinfo : artist date location |
       artist punct date location |
           date artist location |
           artist location date
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has only some possible combinations, but

showinfo: showpart(s)
showpart: artist | date | punct | location
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will allow the showinfo components to be in any order.