So while playing around with a new alchemist alt, I discovered that the last node of Decayology actually gives +10 skill to decay patterns. The tooltip doesn't mention anything about it, but it is definitely there. Going from 29/30 decayology to 30/30 decayology netted me +11 skill to a decay pattern I was looking at. I'm attaching pictures of my current spec on my alt and a sample pattern so you can compare the total skill to the spec tree to see.

I don't know if CraftSim accounts for this extra +10 skill elsewhere or not, but might be more consistent to award it the way you normally award skill through the code.

My alchy alt was a worgen rogue if that matters

It's pretty simple to test on an alt if you don't believe me based on my word (understandable on the internet). Just get a fresh alt to skill 25, get 35 knowledge points from treasures and put 5 of those in alchemical theory to unlock decayology, and put 29 in to decayology, then reference a decay pattern before and after allocating the last point into decayology.

Very interesting! I will put it in :)

After making this, I checked my alts and I had an alt at 26 skill with no knowledge points assigned. I spec'ed 5 into alchemical theory and 29 into decayology, and my total skill was 60 (would have been 59 if I was at 25 skill). Here are attached screenshots of the 2nd alt