Insurance policies for any type structure include the year built. It is a significant factor in generating the cost of the policy. The older the home the greater the perceived risk and the more costly the policy.
Regardless of how the paperwork is detailed a manufactured home is still a manufactured home. For insurance purposes you must get a MH policy. If you insure it as a site built structure and there is a major disaster your insurance company will have a good excuse to not pay. You could easily find that you are not covered, have forfeited any payments made and charged with fraud under states insurance laws.
I learned this in the mid 80s'. My home is a block home to which I joined a manufactured home. For several years I was able to cover it as site built with additions. The fist time the insurance company sent out an inspector that all changed and we have had to pay the rate for a MH policy ever since.
When a title is retired the distinction is ONLY for tax purposes. A MH that retains a title in most states is taxed like an automobile, and an annual license fee is paid. In places where the title is retired the value of the home is added to the value of the real-estate and taxed as if it were a permanent fixture.
Treating a MH as part of the real-estate, in most states, will cost less in taxes as the property appraiser will deduct depreciation annually, just like any other building. A MH as a vehicle is taxed annually by length or weight that never changes.
If the home was insured by the previous owner that old policy will include the year the home was built.
You can also check the local property appraisers web site. They will include the year the home was built