Backdated Liability Insurance
  
A sweetheart deal if you can swing it: buy insurance today and make the coverage begin at a date in the past. This form of policy is not a commonly available coverage, because it increases the risk for the insurance company by extending coverage prior to the date the policy was purchased.
The intent of backdated liability coverage is to cover for claims that may pop up from past business activities. This makes sense if you are buying a "blue sky" business in which the purchase is a building as well as a client base (which is "the blue sky"). A typical backdated liability insurance is usually a commercial general liability policy that provides coverage including claims of bodily injury or other physical injury, personal injury (libel or slander), advertising injury and property damage as a result of your products, premises, or operations. It can be offered as a package policy with other coverages such as property, crime, or automobile insurance.
However, it is expensive by virtue of expanding the length of coverage time and the unknowns that may have occurred prior to the policy purchase.