We've got it easier than the Tigers merger. With no disrespect to the Illawarra faction, the fact that they haven't won a premiership means that no totals need to be added together. Hence, the combined history of the two clubs, premiership tally wise, will equal 16 irrespective of the two clubs having separate histories.
By going with this theory, the Tigers are well within their rights to combine both their premiership tally's and stating the merged club has won 'X' amount of premierships, and I really doubt that anyone would hold it against them at all. I wouldn't.
It is really quite easy to say 'The history of the St George and Illawarra clubs was simply joined as of 1999, and the future records they reach will be tallied onto any of their previous accomplishments.'
Most people mistakenly believe 'Merger' is the destruction of two to form one. Incorrect. Merger is a business term used to identify when two entities join together in an effort to survive and expand. A merger is the continuation of both businesses, only now they have the resources of two organisations instead of one. An excellent example is Coles Myer Pty Ltd. Coles and Myer were separate entities, and simply joined to create one super company. Both retained their history and traditions, so why shouldn't we?