H1B can be extended in 1yr increments when PD is current and I-485 is not filed. This is true for both renewals and change of employer petitions. Renewals can be done until final AOS is adjudicated. Relevant section is 106(b) under AC21.
Some attorneys say that you can still get 3 year extensions under 104(c) if it is change of employer petition. Don’t know if this is true or not.