Accounting policy in bank?

Bank currently is using settlement date for booking of purchasing investment. But I found out that bank used trade date for booking of purchasing investment of $15 million of securities. ( trade date was Dec and settlement date Jan.)
I think that its' Annual report was overstated by $15 million and there was no footnote mentioning accounting change and bank have never used trade date basis for booking of investment previously. Does the bank has to reinstate annual report for last year ?

What is the classification of the investment?
If it is classified as Held at Fair Value through Profit or Loss, the bank must have recognized a gain or loss recorded in the income statement as a result of the change in fair value. If the change in fair value is material, a reinstatement is a must. Else, if no significant change in fair value, no need for the reinstatement as this has been classified as current assets. The reader's of the financial statements may be using liquidity ratios, of which this asset may be part of your current asset convertible into cash. Hence, this has no impact on the reader since if the investment was not accounted, it could have been cash.

If it is classified as available for sale securities, determine if the change in fair value significant affects your stockholder's equity. Changes in fair value for available for sale securities impacts your equity.
Else if classified as Held to Maturity Securities, determine if the classification as current or non current significantly affects the ratios used by the readers of the financial statements. If it is, determine the change in the financial ratios if it would result to a more conservative (low liquidity) or aggressive financial position.

A reinstatement is necessary if the reader's decision would have significantly change assuming the transaction was correctly accounted as compared to what has been accounted.