Hello FelixM,
Any backdating of VAT from before you were registered will have to be included by either manually adjusting the figures for your return, or dating the transactions within your VAT period (making note of the correct date within the description). If you are only accounting for the last 4 years of purchases, your accounts for those years will of course not show correctly - this will be something you should check with an accountant. You can import bills in batch, however these will come across as open, and you will need to mark them individually as paid. You can do this by going to the cog wheel > import data > bills.
Please let us know if you have any further questions.
Thanks,
Talia
