The only time a non-identifying, unsealed letter is required is when the other party has been contacted but has not registered. If the other party has already registered when you did, or registers later, then a sealed identifying letter will be accepted for delivery
Also, when placing an ad in a newspaper, i.e. Winnipeg Free Press, do not use a Free Press Box number as the contact. These box numbers are only kept on record for about a month, and if someone does know some information, but does not contact the newspaper for a couple of months or more, chances are the box number has been given to someone else, and they cannot tell you who had that number when the ad was placed. Use a friends address, your own, or LINKS will let you use our address so that months later, if someone comes forward with information, the contact address is still valid.