The assessment needs the rebate in the version actually applied. Preserve the agreement, price lists, rebate scale, thresholds, purchasing shares, reference periods, payments and every rule for later settlement. Drafts and later changes should remain separate from the version in force at the relevant time.
For the market side, product and geographic definition, market shares, competitors, alternative sources, switching costs, supply capacity and customer dependence may be relevant. For each customer, demand, purchased quantities, realistically switchable units and the economic importance of the benefit should be traceable.
Invoices and tables show the price but do not always explain the loyalty effect. Add emails, meeting notes, internal approvals, forecasts, complaints and data exports. A chronology connects the rebate conditions with actual purchasing decisions.
Where a competitor alleges harm, preserve market developments, lost orders, failed expansion attempts and alternative explanations separately. The article on cartel damages after price fixing addresses the separate claim path for loss.