TLDR: You must use the result or results of the accounting periods closed during the tax year. If several balance sheets are closed during that year, you add their results algebraically.
Determination principle
When your accounting period does not coincide with the calendar year, taxation is in principle based on the result of the accounting period closed during the tax year.
Accounting period of less or more than twelve months
If the accounting period closed during the tax year lasts less or more than twelve months, the tax is nevertheless assessed on the basis of the result of that accounting period.
Several balance sheets closed in the same year
If you close two or more accounting periods during the same tax year, the results of the relevant balance sheets are totaled. The taxable base corresponds to their algebraic sum.
You must therefore take into account all the results of the accounting periods closed during that same year, without attributing them separately to each of the periods covered by the accounting periods.
Point to note
The rule depends on the closing date of the accounting periods and not solely on their duration. Therefore, check which balance sheets were actually closed during the relevant tax year.