Bilby
Executive Chef
Brown sugar shouldn't make the difference, nor the colour of the egg. Personally I don't soak my dates when they are diced, but would if they were in large pieces or whole. Sounds like you used too much bicarb. Wouldn't expect a date loaf to double in size, but I am prepared to be corrected by better cooks than I, and that may be why it is drier. If you feel like experimenting, you could always omit the bicarb. It just won't rise as much.