The reason why this date of 1 March 2025 is set is shown here
https://kb.bpsoftware.net/bppremier/spectra/Clinical/Immunisations/RecordImmunisations.htm

The Australian Immunisation Register (AIR) is introducing mandatory changes to simplify the Vaccine Type field. Effective from 01 March 2025, only the following options will be available:

• NIP/Commonwealth
• Antenatal
• Other

The options for Private and State Program have both been replaced by the new option ‘Other’. Where you previously would have selected the Private or State Program option, you will now select ‘Other’.

Submitting a vaccination encounter after 01 March with a Vaccine Type of Private or State Program will result in an error.