To determine what potential offerors would have reasonably expected, consideration should be given to the procurement format used, the history of the present and related past procurements, and the nature of the supplies or services sought. A variety of factors may be pertinent, including: whether the requirement was appropriate initially for an advertised or negotiated procurement; whether a standard off the shelf or similar item is sought; or whether, for example, the contract is one for research and development, suggesting that broad changes might be expected because the Government's requirement are at best only indefinite."