I'm no expert on Simonsen, but according to the stub on Wikipedia, he submitted this symphony for the 1928 Olympics in Copenhagen -- and won. (The modern Olympics had arts competitions for its first 50 years.)
Also, if the musical content of this symphony were in fact published in 1910, when the composer turned 21, the work's impact on both Sibelius (who had not yet written his fourth symphony) and Nielsen (Simonsen's teacher), who had not yet written his third, would have to be taken into account in all future discussions of those composers.
In short, I suspect 1910 is a typo (perhaps an old one in the Sibley catalog), and that the real publication date is closer to 1930, with all that implies for copyright.
