When the books say something will tolerate part-shade, or light shade,
is there any difference between a continual dappled sunlight, or a
corner that only gets sunlight for an hour or two a day, but full sun
when it does get it?

Also, if you have a place that gets no sun at all except for 4 months in
the summer, and for those 4 months it's good sun for up to 8 hours a
day, could you put in a plant that says it needs full sun? We just
happen to have a house at the bottom of our short South facing garden
that stops most of the sun until it gets high enough in the summer to
clear the top of that house. It occurred to me that as many plants are
dormant in the winter they might only care what they get in the summer.