As to what goes into the peat-free, or even the peat-based (which may not be 100% peat), it could vary widely between manufacturers. I bet that no two manufacturers will have identical "blends", and even the same manufacturer will be slightly different from one year to the next.
The best source of information regarding content of the composts would be from the various manufacturers. The product bags may include an e-mail, or website, or telephone number, or address where you can direct queries.