Data converted Service Contract not available for any additional update through OM

We are using Service Contract functionality through OM. We have done the contract conversion using contract API.  Further to this, Users want to update the data converted contract for adding lines / sub lines through OM. We are not able to find any data converted contracts in the navigation: Order Management > Lines >Actions > Service Contract Details > Existing Contract.

If we create new service through Om, these contracts are available for update. (Using Existing Contract)

Service contract module has all our converted contracts to work with same customer and contract is in active status.

 What are the criteria OM Use to make the contract available for update through OM?