Is there an update that I am missing?
No. Your gallery display all images in your Flickr account with the tag 'birthday' but your Flickr link above displays a Flickr set (two different things).
If you have tagged all the images in the set with the tag 'birthday', then both selections should contain the same images. However, if you have recently tagged any images, it may take some time for the tags to propagate through Flickr's system and for the tags to show up in API searches (such as that performed by SimpleViewer to fetch the images from Flickr's servers).
At the moment, if I enter the Flickr details you use in your gallery (Flickr User Name/Id and 'birthday' Tag) directly into Flickr's own API Explorer, 32 images are returned. This is the same number of images that are displayed in your gallery.
You could double-check that all the images in your set have been tagged correctly and then wait (perhaps up to 48 hours) for the tags to take effect.
Otherwise, if you just want to display the set, you can enter flickrSetId="72157640202660364" into your gallery's Pro Options text area. (flickrSetId overrides flickrUserName, flickrUserId and flickrTags.)
SimpleViewer Support Team