It all depends on what you mean by "Flagship".
The original ST3 is this one:
http://www.ikmultimedia.com/products/sampletank3/with over 4,000 instruments and a 33 GB sound library.
I presume that that is what you have.
The SampleTank 3 MAX edition http://www.ikmultimedia.com/products/stmax/adds instruments to the above; it includes over 4,600 instruments and 52GB of samples.
SampleTank 3 SEhttp://www.ikmultimedia.com/products/sampletank3se/is a fully functional, affordable special edition of the ultimate sound and groove workstation with a 6.5 GB instrument library.
SampleTank 3 Custom Shophttp://www.ikmultimedia.com/products/sampletankcs/ is the fully functional FREE version of SampleTank 3 that lets you purchase, download, edit and play instruments from the entire massive collection of SampleTank 3 add-on instruments. It comes with 30 fully editable instruments.
As for updates, if your software is working OK, then you do not need them. Otherwise, for IK Multimedia products anyway, it is easy just to check the Releases in your User Area / My Products section.