While many companies provide forecasts, they all adjust their projections toward the NASS estimate as the season progresses. Objective yield forecast variables for number of fruit and weight per fruit. It is also worth noting that the NASS data is public information and is freely passed to all. It does rely on producer involvement. For the cost of time to participate, the producer gets the benefit of market information to use in planning.
Private firms do forecasts for their own reasons.
One is to generate business. It is important that producers evaluate the source of data they use, particularly if an estimate comes from a company involved in futures and options trading. There are potential conflicts of interest that can influence their forecasts. Every Monday morning during the growing season, NASS releases a report on crop progress and conditions. For the major commodities in major producing states, this report briefly details crop planting, percent of crops at various stages of maturity, and percent harvested.