Davies notes five principal reverses for sixpences 1887-1893 labelled A to E and also mentions that "Numerous design & die sinking differences exist before adoption of rev. 'D'.". What is not mentioned is that there are 2 obverses and the changeover seems to have occured during 1889. The picture below shows the difference between obverses 1 and 2, left and right respectively. As long as you can focus that close, you can see the difference with the naked eye. The difference is a wedge cut out of the truncation above J.E.B. which is present in obverse 1 and not in obverse 2.
I'm not entirely certain which crossover die pairings exist for 1889 but I have seen 1+C, 2+C, 2+D and even 2+A, so it is possible that all permutations are out there. As far as I'm aware all obverses after 1889 are obverse 2, unless you know different.