Once they come out of administration though doesn't everything change and they then need to refund due to consumer law. If not I'll be using Credit Card chargeback option.
Nope, think of it like three separate companies. (I've given them all a name in brackets to make it easier to explain)
Virgin Australia before 21 April (VA1) - Before Admin
Virgin Australia between 22 April and 31 October (VA2) - During Admin
Virgin Australia after 1 November (VA3) - Owned by Bain
If you had a booking before 21 April then your contract was with VA1. VA1 has since collapsed and technically no longer exists therefore technically your money/bookings are gone. Normally you'd line up as an unsecured creditor and probably get cents back in every dollar from your booking however an agreement was reached that because everyone is getting a Future Flight Credit then you won't be eligible to claim as an unsecured creditor.
When VA1 collapsed, VA2 (the administrator) stepped in and took over the business to continue running the company whilst looking to sell what remained of VA1. VA2 sold the company to VA3 (owned by Bain) with the condition of honoring existing booked flights during the time when VA2 was operating.
Bain (VA3) also agreed to provide a credit to those who held bookings with VA1 but this is basically a goodwill credit, technically bain could provide you nothing if they wanted to.
VA3 is a new company owned by Bain, any tickets purchased whilst VA2 or VA3 was in operation are subject to normal fare conditions because you're technically dealing with a new company who legally can provide refunds.
People with VA1 booking could ask Bain for a refund but that will achieve nothing given you're essentially asking a new company who you've never done business with for them to give you money.
Regarding Chargebacks, if you're still within the timeframe then that's up to your bank. Many banks aren't allowing chargebacks relating to COVID-19 and you might be outside of the timeframe depending on when you purchased your ticket.