Thanks for your prompt response.
The reason which I asked this question is I got my 'In Canada Approval Letter' for my work permit and started my job but was not sure that I should share the same SIN (as it is still valid to end of this year) with my new employer or I need to get a new one.
As I have understood from your explanation, I can share my current SIN and just renew and update the expiry date of it before it will be expired. Correct?
BTW, Thanks a lot for your help