This link might be helpful http://www.coins-of-the-uk.co.uk/halfp.html
I had trouble finding stuff online myself so I bought The Bronze Coinage of Great Britain by Michael Freeman and it has helped me. Between 1860 and 1894 there were 19 different obverses and reverses for the half penny, mostly with small differences like you were noticing. Your 1889 in particular only had one die pairing that year, the 17th obverse and 19th reverse, represented by the letter S in the book.























