Complex sentence: He purportedly learned this tuning from his musical mentor, the unrecorded bluesman Henry Stuckey, who in turn was said to have acquired it from Bahamian soldiers during the First World War, despite the fact that his service card shows he did not serve overseas.
Split into simpler sentences: He purportedly learned this tuning from his musical mentor, the unrecorded bluesman Henry Stuckey. Stuckey in turn was said to have acquired it from Bahamian soldiers during the First World War, despite the fact that his service card shows he didn't serve overseas.