Currently, this works:
{contributors-summary:page=FAQ|spaces=help|scope=descendants|groupby=pages}
These do not:
{contributors-summary:page=help:FAQ|spaces=help|scope=descendants|groupby=pages}
{contributors-summary:page=help:FAQ|scope=descendants|groupby=pages}
{contributors-summary:page=help:FAQ|groupby=pages}
If no 'spaces' are specified, one would expect that Help:FAQ should work, to be consistent with most other plugins.
If spaces are specified, I'd suppose you'd have to ignore the 'Help:' in this case and look for FAQ in each space?
Improvement
Open
Minor
allow stats from pages other spaces to be collected by specifying a page in another space