Complex sentence: In 1966, "Trumpet" received enough nominations for inclusion on that year's final Hugo Awards ballot, but was later ruled as being ineligible because it didn't meet the Hugo's minimum number of published issues requirement needed for nomination.
Split into simpler sentences: In 1966, it received enough nominations for inclusion on that year's final Hugo Awards ballot. But "Trumpet" was ruled as being ineligible that year because it didn't meet the Hugo rule's minimum number of published issues requirement needed for nomination.