I was just on the Agent VAT portal (the old one, haven't touched MTD yet) as I'm doing very late accounts for a last minuter. I needed to see the figures filed for the first two quarters of the financial year but, with the accounts being so late, they're not shown under "view submitted returns".
Anyway, I discovered that if you click on the oldest one available, the URL for the page will be https://www.tax.service.gov.uk/vat-file/trader/<VAT number>/period/###/return where ### is a three digit number. This is the number of the period and older ones can be accessed by manually changing this to the number for the earlier period.
I think the number is the month  so to access my older periods I took three off, then three off again to get the two quarters prior to the one I was linked to. Thought it might come in handy for anyone else with a similar issue, I have no idea how far back you can go but you can at least get a couple more than they'll link you to.