Glad to help.
This is one of many designs that I haven't yet got round to sorting out in my collection.
It has all the usual complications (watermark, perf, shade) along with the stereo/electro difference.
Here's a more complete breakdown with two more watermark (W) types and a correction to include "partly missing triangles".
I see (in SG Part 2, 2009):Type 2:
SG 14-19 1874-80 recess - no watermark
SG 25-28 1881 recess plate 1 - sharp triangles - W 3 (kr in circle)
SG 29-32 1890 recess plate 2 - blurred or partly missing triangles - W 3.Type 4:
38a-38i typo (litho background) 1888 printed from stereotypes - W 3
39-51 typo (litho background) 1889-98 printed from electrotypes - W 3
SG includes diagrams and several paragraphs of description to distinguish the stereotype and electrotype stamps by means of characteristic flaws and other details.
I assume the following Type 4 stamps are also typo (litho background):
52A-63A 1898 medium white paper - W 6a (crown in oval)
52B-63B 1899 thinner yellowish paper - W 6b (crown in circle)
SG mentions (but doesn't list) two versions of watermark W 3 which differ in the height of the letter "k".
I have around 60 of these stamps including duplicates so I have a long way to go!
I guess this may stay on my "too hard" list unless I treat SG 52-63 as a single set.
My "too hard" list already has quite a few entries including the paper differences in the Portugal and Colonies "Ceres" stamps and the watermark differences in the South Australia W 10 and W 13 stamps.