@ehsteve, your two examples have very different semantics though.  In the first case, a date range is a contiguous block of time.  In the second case, there is no guarantee about the time-contiguity of the files.  The first should be a single light curve, but without the user forcing it, the second should not be.

This brings about a few other related points:  
1.  What should happen if the times are _not_ contiguous and the user wants them concatenated?
2.  What should happen if there are gaps in the available data (from the provider)?  One large LC with 0's or should it break at the gaps?
3.  What happens if the sample rates are different?  (Does this happen in real data?  I'm asking out of ignorance...)  If they can be different, how does that represent in the concatenated light curve?

(This is all good discussion, btw.  It is good to hash this out now, as I was sort of making it up as I went with the Map() interface.)