Hi Aran,
I am glad you enjoyed the beginning, at least.
Could you explain which organic builder you are using and more information about what you exactly did?
The latest version is here :
https://github.com/BertrandDechoux/OrganicBuilder/tree/developStage 9 is indeed doable with the single rule "a1d1 => a1 + d1".
The reaction does work correctly using this single rule.
It however appears that there is a old bug with the validator.
The evaluate button will not confirm the success.
It is now fixed with the latest version.
I am not able to reproduce any error with stage 12 and the rule you provided.
Regards
Bertrand