In reply # 13 peter_conole mentioned the 5 unpublished symphonies by the Belgian composer Hendrik Waelput. I happen to have an old radio broadcasting recording of Waelput's 2nd symphony. It might be unfair to judge his symphonic output by one performance of one symphony but I think the neglect of this composer is not entirely unjustified.
On the other hand I think the 5 symphonies by an other Belgian composer, Josef Ryelandt, deserve more attention than they get nowadays.