Snapshot not picking up new articles in SQL Server 2012 transaction replication when added through script

Question

I am trying to add new articles to an existing publication in SQL Server 2012.

I am adding the article to the publication with the syntax

--add the table into the correct publication
sp_addarticle @publication='<publicationname>', @article='CardBookingType_tbl', @source_object='CardBookingType_tbl'

Previously on SQL Server 2008 I used to use the following syntax to subscribe to 1 table only and then run the snapshot. This no longers work on SQL 2012 as you have to subscribe to all articles.

--add the table into the subscription
EXEC sp_addsubscription
        @publication = '<publicationname>',
        @subscriber = '<Servername>',
        @destination_db = '<dbname>'

GO

In SQL Server 2012, if I add the table via the GUI and then run the snapshot agent it picks up the new table fine. But if I add via the script it appears in the gui but the snapshot reports no new items were detected.

Seems like I am missing a piece of code to flag the subscribers as missing a article?