WowAce

The library LibArtifactData-1.0 can be used instead. Change event.lua line 988 to:

--    local _, amountArtifactKnowledge, _ = GetCurrencyInfo(Garrison.GARRISON_CURRENCY_ARTIFACT_KNOWLEDGE);
-- In 7.3 Currency is no longer valid as Artifact Knowledge is now system-wide
    local LAD = LibStub("LibArtifactData-1.0")
    local amountArtifactKnowledge, knowledgeMultiplier = LAD:GetArtifactKnowledge()

and add LibArtifactData-1.0 to the TOC and .pkgmeta as described in https://github.com/Rainrider/LibArtifactData-1.0/wiki/How-to-use

Instead of expanding the table Garrison.ARTIFACT_KNOWLEDGE to contain the new multipliers, LAD:GetArtifactKnowledge() returns that value directly (as shown above) and the table and lookup could be eliminated.