Correctly dealing with and reconciling to ATO ICA; Effective Date vs. Processed Date?

Prepare yourselves for a tale of woe.

My accountants of 15 years turned out to have quietly maintained a second set of books. Whenever they found an issue in my MYOB file rather than tell me about it or offer to fix it, they silently did whatever was required to prepare the accounts and company tax return, and ignored the issues in MYOB.

This included failing to properly deal with all of the tax-related MYOB accounts: GST Paid and Collected, PAYG Withholding, and GIC penalties and penalty remissions. Most notably there was simply no ATO ICA account in MYOB at all.

You can imagine the mess. I am no longer with those accountants. My next accountant started the process of working with me to correct this in MYOB - I now have an ATO ICA liability account and all BAS/IAS are entered into it, and payments to the ATO are shown as payments to the ICA liability account in MYOB. So far so good?

To my sorrow this excellent accountant retired and I moved to a third set. This new one disagrees greatly with how the second one fixed things. The chief disagreement is about reconciling the MYOB ATO ICA liability account to the actual ATO ICA.

The second accountant said that this should be based on the ATO Effective Date. The third client says it should be based on the ATO Processed Date.

e.g. if I revise a BAS for the 2020-21 financial year in the 2021-22 financial year, which of the two ATO dates should my balance sheet match as of 30/06/2021? The third accountant argued persuasively that it should look like what the ATO thought it looked like at that time, i.e. reconcile to the Processed Date, and this intuitively makes sense to me. The second accountant said that since the amendment was made before the accounts and tax return were prepared, the reconciliation should be based on best knowledge at that time, i.e. reconcile to the ICA balance Effective Date as of 30/06/2021.

I am now hopelessly confused because using Processed Date (that's surely what "as of" means, right? This is what both my company and the ATO thought the numbers were as of that date) is not correctly balancing GST Paid, GST Collected, PAYGW, etc. I would have thought that if all of this was done correctly they would have a NIL balance in the balance sheet and not appear at all, because all liabilities were transferred to the ATO ICA liability account.

I know the usual advice for these sorts of things is "ask your accountant" but three sets of accountants all have given me wildly differing approaches... and none of them seem to properly reconcile to the ATO's numbers. I would be most grateful for anyone who can make some sense of this.