The most common example of this is revenue/sales. For any given company, on a historical basis, Thomson Reuters collects either Net Sales or Gross Sales, but not both, depending on the company's own reporting practices. Historical net sales strictly represents sales receipts for products and services, less cash discounts, trade discounts, excise tax, and sales returns and allowances. However, the approach of analysts may differ from this standardised approach.
An example of this is Imperial Tobacco where the only available consensus estimate for sales is a company specific definition of net sales, as defined here, "Tobacco net revenue comprising tobacco revenue less duty and similar items, excluding peripheral products". The majority of analysts covering Imperial tobacco use the above mentioned basis for forecasting, hence it is used for the consensus sales forecasts.
If you notice an inconsistency between historical and forecasts financials, do feel free to raise a ticket and we will look into any company specific factors that may be at play here.