Complex sentence: They were relegated from the First Division in 1929 and have spent a further 8 seasons in the first tier since, the most recent return was a one-year spell in the 2013--14 season.
Split into simpler sentences: They were relegated from the First Division in 1929. Since then, they have spent a further eight seasons in the first tier, the most recent return was a one-year spell in the 2013--14 season.