Can we generate attributions and Removal effects without 'Start' state

[naadvar]

Hello ,

I am currently trying to model a Marketing Multi-Channel Attribution. All the articles and the packages I have come across use a special "start" state and the removal effect is calculated based on that start state

My question primarily is of two parts:

1. Can we consider the first touch as the start state of each path.
2. How can we calculate the removal effect if there is no "start "state( any documentation or an explanation of the formula would be really helpful)