Cap-subject - The petition needs to be filed in April and may be subject to lottery, if that happens
Cap-exempt - The petition can be filed anytime. Transfers and extensions fall under this
You can have as many cap-exempt petitions filed until you have stayed inside US for 6 years on H-1. Thereafter, you need to cool-off 1 year outside US and file a cap-subject H-1 petition. If you leave now, then this petition can be filed in April 2017 for a start date of Oct 2017.
However, if your green card is under process and has reached a certain stage, then you can file cap-exempt petitions even after staying for 6 years inside US on H-1.