We should basically have a consistent way for representing CDA dates in JSON, which can handle:

* single points in time **including precision** (e.g. `2004` is 1-year precision , `2004-10-19` is 1-day precision)
* ranges with start and stop

This is how I coded it for the SMART C-CDA receiver:
https://github.com/chb/ccdaReceiver/blob/nodejs/lib/ccda/ccd.js#L103

Example: 
https://github.com/chb/ccdaReceiver/blob/nodejs/samples/samplenew.json#L156