I hope it is helpful for you. I am not sure if this is right answer for you because I have limited information.
First of all, please check the number of return-sets. if the return-set has more then 50 dataset, result could be same. (might count param. -1 = unlimited in the rest API of WCA (Watson Context Analytics)
Second, if you can check the log from the server side, you can see the full query which manipulated from WATSON engine.
Last, I am not really sure that watson REST-API can recognize 'now-2w' style start-end form. Would you please link the tutorial? In my previous project, I wrote the start-end date by Y-M-D form.
Good Luck
