Green Card process - Calculation of 6 years

H1B visa has a 6 years limit to stay in US. Please clarify my doubts.

I came to US on Feb, 2012 and i have completed 3 years (L1B - 1 year and10 months, H1B - 1 year) in US by this Feb, 2015.

Last time i visited US on L1B Visa couple of times.

  1. 2003 - 6 months
  2. 2006 - 1 year

Currently my employer is in the process of starting my GC process next month, but they calculated my US stay and saying that i have stayed 4.5 years in US already. I have a limit to stay in US till september, 2016. But I have not stayed 4.5 years in US continously and thought that i have another 3 years to stay in US. Otherwise i should have started my GC process last year itself. Please clarify whether my employer is correct on the calculation of 6 years.