Is it possible to post a bill in to a previous tax period (that is closed) but a current accounting period (that is open)? The tax period fields are not exposed on the transaction record

Date is used to decide which tax period it will use.

okay so If I use 31.03 (March Tax Period) in the date field and then choose April in the accounting period, it will work? Even if the tax period has been closed?

Transaction Date, Posting Period and Tax Period are linked. If the Transaction Date (31st March) is in an Open Period and Open Tax Period, it will set both to "March 2019". If the Tax Period is closed, it will post in the next Open Tax Period, but if the Posting Period is closed, usually it disallows it (based on your Account Preferences).#

What is the benefit/function of having a separate tax and accounting period function if not for transactions where the VAT and the accounting period need to be different?

When your Tax and Fiscal Years do not align

Acknowledge that but they cannot operate independently of each other

They can, but the 43003 Tax Bundle recalculates the periods and dates and overrides it... but if you disable the scripts, you can do whatever you want 🙂

The next suitetax release exposes the tax point date on the transaction records. #2019.1😁