@mike.kovacs - you bring up a valid concern. This is definitely something that needs to be considered. Having good/better/best targets for different phases of the development is an excellent idea.
For reference, Denmark (Ny aftale: CO2-krav til nybyggeri fra 2023 | Ingeniøren) does ratchet down in the following way:
- 12 kgCO2e/m2/yr is the benchmark
- 8 kgCO2e/m2/yr in 2023
- 7 kgCO2e/m2/yr in 2025
- 6 kgCO2e/m2/yr in 2027
- 5 kgCO2e/m2/yr in 2029