Analysis of information sources in references of the Wikipedia article "Symphony No. 9 (Schubert)" in English language version.
... The several points of the case may be summed up as follows: 1. That Schubert certainly contemplated writing a grand Symphony in 1824. 2. That he probably wrote such a work at Gastein in 1825... 5. That he probably revised the work in March, 1828, with a view to performance...