"discussed therein" is correct and can be used in written English.
It is a formal way to refer back to something previously mentioned. For example, "In the previous section, the new policy was outlined. The implications of the policy were discussed therein."
1. See Stanley 2011 and his opponents discussed therein.
One of the topics discussed therein, how and why Square Enix decided to bring the game to the Xbox 360.
The title 'metaphysics' literally, 'after the Physics' very likely indicated the place the topics discussed therein were intended to occupy in the philosophical curriculum.
Stability, partition of the parameter space and the equivalence of mosaic solutions with a multiple shift space are discussed therein.
In a study publicized during a 2014 security conference in Hamburg, researchers demonstrated how hackers could insert themselves into a device's call-forwarding function, redirecting calls, and any private information discussed therein, to themselves before bouncing them back to the receiver.
The ability of imaging algorithms to incorporate multiple types of data and use advanced inverse techniques borrowed from meteorological data assimilation to produce four-dimensional images of electron density is discussed therein.
The year 2011 2012 witnessed a plethora of special issues of journals on the return of results, but only a few articles therein discussed the particular situation of population studies that serve as a resource for future unspecified research.
The cases documented therein — and discussed at today's meeting — are a reminder that the path peace via development is a highly local challenge, where solutions vary by context.
Some of the practical issues therein are discussed.
In fact, a general inequality for the projection constant of a real or complex n-dimensional space is obtained and the question of equality therein is discussed.
Therein, the discussed problem of hydrogen interchangeability (see Extended CSP formulation) is faced again and would result in symmetric overall atom mappings.
