Attribution is always a tough model to get right, and there are so many different organisations using many different methodologies ranging from first action attribution, last action attribution to weighted attribution.

A new theory from a few predictive analytic companies are for organisations to adopt models already in place at many consumer-focused organisations; Test Versus Control Analytics. 

The concept is simple in theory: compare the performance of accounts that received a given marketing touchpoint (‘test’) with highly similar ‘control’ accounts that did not. The difference in performance (e.g., the relative change in the total value of their transactions) between the two groups after the marketing touchpoint (e.g. event attendance, email campaign, etc.) can then be confidently attributed to the action.

I'm not sure this is the silver bullet, but certainly worth looking into as a potential way of evenly attributing the ever growing channels and touch points in the ever complex B2B marketing mix...