H1B to O3 to H1B Possible

[Mig]

Dear Friends - Below is the situation

1. 2005 - Came to US on F1

2. Oct 1st 2008 - Moved to H1B with COS with Company A

3. April 2010 - Moved to H1B with Company B

4. July 2010 - H1B visa stamped on passport with Company B name. Visa was granted till April 2013 (Question 1 below)

5. Feb 2013 - Moved to O3 visa

6. June 2013 - Received offer letter from Company C (Question 2 below)

Question 1 - Since my COS in event 2 was till Sept 2011, why did the visa officer grant me a visa till April 2013? Is this normal?

Question 2 - Can I join Company C? Since I have not exhausted 6 years of H1B, am I correct to assume that I am exempt from cap?

Thank You

Mig