I am currently on my 7th yr H1 working for Emp A with I-140 Approved. I got a job offer from company B who is willing to transfer my H1 but won't process GC. I know I will get 3 yrs extn based on I-140 approval. My Current company A is willing to keep my I-140 active.

What happens after 3 yrs from now when I am ready for H1-B extension with Company B or H1-B transfer to Company C. Will I get unlimited H1-B 3 yr Extenstions based on my I-140 Approval or 3-yr extn is only one time from Company A to B.
Please clarify.