G'day Tom,
Yes.  I have done all that.  It has a FT index and I am already trying to search by field.  That's how I got the "DatesSighted is on 25/07/2015" token.  It works fine for a single value field but does not work for the multiple value field as per my original post.
Even though it is a multiple value field there's no option for "contains" only the regular date options "is on", "is before", etc.