Obviously if it had the centerfold the book would grade higher. 1966 is written in looks to be pen on front cover. Comic retailer most likely put it there.
Fairly common to write or stamp date on book during the 1960s. Batman 181 CGC 0.5 Looks Much Nicer Must See Pics 1st Appearance of Poison Ivy. The item "Batman 181 CGC 0.5 Looks Much Nicer Must See Pics 1st Appearance of Poison Ivy" is in sale since Wednesday, May 13, 2020. This item is in the category "Collectibles\Comics\Silver Age (1956-69)\Superhero\Batman". The seller is "lowest_price_collectibles" and is located in Carmichaels, Pennsylvania.This item can be shipped to United States, Canada, United Kingdom, Denmark, Romania, Slovakia, Bulgaria, Czech republic, Finland, Hungary, Latvia, Lithuania, Malta, Estonia, Australia, Greece, Portugal, Cyprus, Slovenia, Japan, China, Sweden, South Korea, Indonesia, Taiwan, Thailand, Belgium, France, Hong Kong, Ireland, Netherlands, Poland, Spain, Italy, Germany, Austria, Bahamas, Israel, Mexico, New Zealand, Philippines, Singapore, Switzerland, Norway, Saudi arabia, United arab emirates, Qatar, Kuwait, Bahrain, Croatia, Malaysia, Brazil, Chile, Costa rica, Panama, Trinidad and tobago, Guatemala, Honduras, Jamaica, Aruba, Belize, Dominica, Grenada, Saint kitts and nevis, Turks and caicos islands, Bangladesh, Brunei darussalam, Bolivia, Ecuador, Egypt, French guiana, Guernsey, Gibraltar, Guadeloupe, Iceland, Jersey, Jordan, Cambodia, Liechtenstein, Luxembourg, Monaco, Macao, Martinique, Nicaragua, Peru, Pakistan, Paraguay, Viet nam, Uruguay.