I don't think this has come up so far in the forums and I couldn't see a thread already started to list these sorts of things.

#552 - Accomplished 達

Hesig gives the stroke count as 12 which agrees with the large kanji in the box. The error is with the series showing the writing order. It only uses two horizontal strokes for the sheep primative leading to a stroke count of 11.

I asked one of the teachers at school and he said it should be 12.

The only time I can find the two stroke primative is in a very similar kanji 逹. This has two dashes on the left and so ends up with the same stroke order. I can only assume that they got mixed up during editing (although I don't think the second kanji is in RTK1)

逹 is a variant (nonstandard) form of 達. The 辶 in 逹 has two strokes because basically the Joyo-kanji were revised so that the "road-way" radical only had one drop and all the more rare kanji (including old forms and variants) were left with two drops. So it's only coincidental that 逹 and 達 both have 12 strokes and the stroke order diagram is a plain mistake.