Just tested Three Bridges to Norwich Off Peak Return on the Southern site and it doesn't allow departure from Three Bridges until 0942, meaning you miss the first few Off Peak trains out of Liverpool Street. However, Three Bridges to Birmingham Off Peak Return allows you to travel from Three Bridges at 0806 so you can make the first Off Peak train out of Euston.
Surely this inconsistent application of the 'Network Area' rule is something that ought to be raised with ATOC as a matter of urgency? Presumably lots of people are unnecessarily paying Anytime fares as a result?
Three Bridges - Norwich has restriction code 7B as discussed earlier. As written, this restricts both legs of the journey and it appears that it is interpreted in this way by journey planners.
Other restriction codes only include restrictions on the leg outside of the Network area (i.e. the 9I restriction on a TBD-BHM SVR restricts only trains
leaving London on the outbound, and
arriving London on the return). Thus there is no need for the journey planner to understand the Network area rule, as it is implicit in the restrictions.
I'd agree that it certainly does need amending ASAP, and
I hope that this situation has arisen through laziness and general incompetence in writing the restriction - and trying to have a single text apply to both journeys out of, and in to, the Network area - rather than a deliberate attempt to further restrict Off Peak validity.