For a 1930's build house, how soon - or would you - expect to see water damage if you get flooding to within an inch of the damp course ? (patio was 4-5" below water approx)
...either to foundations / internal floors which are unlikely to have a damp proof membrane etc.
If not as a one-off, how about on an ongoing basis at least annually now ? (slip / heave etc. - we're in a clay soil area)
If this was a "new" phenomenen caused by the erection of a new building that effectively created a dam against the natural drainage of the land for the proceeding 70 years, who could you claim against ?