H1B extension before 6 yrs cap with approved I-140

[stepinasfriend]

I was on L1B for a year, converted to H1B and been in H1B for 3 years,
total L1B+H1B is 4 years. My H1B is expiring in 4+ months from now.
I have PERM and I-140 approved. All this have been with the same
employer. My employer started H1B extension for due 6 yrs (i.e next 2 yrs).

Question: Since I have I-140 approved, as part of H1B extension, can my
employer extend H1B for 3 years ? Or can they extend only due 6 years (which is 2 yrs) ?

Thanks in advance.