H-1B, Returning to company who began green card application

Hi,

I was just laid off from my job. I was there 18 months and I had transferred my h-1b. Now my old company who I left is willing to take me back. They told me my green card application I filed there is 'still going'. I didn't think this was possible as I left the company that was sponsoring it. Any ideas? should I reapply to be safe? is there a limit to the number of green card applications you can have at once?

Any info/advice would be greatly appreciated. Thanks!