The first accounts for a limited company are from oct 19 to oct 20 (13 months) to coincide with statutory filing. Only appears possible to setup a 12 month period in QB?

Another way to handle it is via two journals. For example say the company started trading on June 20 2020 and the year end will be 30 June 2021. 

On 30/6/2020 you post a Journal that zeros out all accounts of the Balance sheet and the PL. You then post a reverse of this journal on 1/7/2020. This way all your balances of the short month have been transferred to the 12 month period. make sure that if there are any multi currency accounts involved that you use the same exchange rate for both journals in order not to have any exchange gain/loss by the posts. 

The neat thing is that if you don't have any other bookings on 30/6 and 1/7 you can still get the exact June end balance with a report from 1-29/6 and the exact 12 month balance from  2/7/20-30/6/21. Still all your normal 12 month year reports will have the full exact 13 month balances.