The high bid displayed in the average historical bid range represents the highest amount that an advertiser has bid in recent days and/or weeks for a particular keyword. For example, suppose that an advertiser placed a $10 bid on a particular keyword. For the time period covered by the Average Historical Bid Range, this $10 bid was the highest bid. However, the advertiser changed this $10 bid after one hour. If you look at the Latest Available Bid Range, you would likely not see this $10 bid (unless you happened to look during the hour that the bid was active).