It is a bit unclear when William visited his brother on Zanzibar and the long delay in the publishing of these unsigned and undated sketches, (not published until the late 1800's) makes dating these works difficult.
Kidogo si dhahiri/wazi ni lini William alimtembelea kaka yake Zanzibar na uchelewashaji mkubwa katika uchapishaji wa hii michoro ambayo haikuwekea sahihi wala tarehe, (haikuchapishwa hadi mwishoni mwa miaka ya 1800's) yote haya yanaifanya kazi ya kuiwekea tarehe michoro hii iwe ngumu.