[NB]

One more question:
Do I need to get the new reference letter till Aug'17 or the previous one will work FEb'17. As I am getting extra 5 points if I count this duration of work ex.

Get an updated reference letter and keep it in your records
No need for reassessment as Scorpion has advised

You may need to submit it to the CO in case he asks for the same during verification

Cheers