I looked at the Southern (only) Super Off Peak Day Return, the absolute lowest fare to London Victoria (see attachment). The Southern website does not (to my knowledge) show restriction codes.
The terms and conditions for this fare are these (extract):
Super Off Peak Day Return
Ticket Description:
Super Off-Peak fares are cheaper tickets for travelling on trains that are less busy. You may be required to travel at specific times of day, days of the week or on a specific route.
Break of journey:
A break of journey is allowed on Super-Off Peak Day tickets unless otherwise indicated by a restriction shown against the ticket's Restriction Code.
Validity:
... Super Off-Peak Day tickets are valid for travel on the date shown on the ticket and until 0429 on the following day, by which time all travel must be completed. Time restrictions are indicated by a restriction shown against the ticket's Restriction Code. Travelling via London. If the route shown on the ticket has a + the ticket includes the cost of travelling between certain London Stations (e.g. between Liverpool St and Paddington) by either London Underground, Docklands Light Railway (DLR) or First Capital Connect (Thameslink Route) services appropriate to the route of the journey being made. Tickets will only be accepted by London Underground and DLR on the date shown on the ticket and until 0429 the following day. Other than to change trains, a break of journey at intermediate London Underground or DLR stations is NOT permitted. Travel restrictions do not apply on public holidays.
Train operator:
Southern Railways
So, considering that the Southern website offers no other information concerning restrictions (no codes are mentioned) it's clear that break of journey is permitted on this, the lowest of all fares.