For two serial numbers (we have three, for some reason...) the first option doesn't exist, but instead I get "Symantec Protection Suite Enterprise Edition 4.0" which results in an empty download list and the "Update..." option.
For the third serial number, the "Symantec Endpoint Protection 12.1" link is there, but the available downloads presented appear to be even older - dated May 26 2011.
Clicking through that option dated May '11 does, however, result in links to 12.1.4.1a. I'm not sure why Symantec would expect users to click on something clearly marked as May 2011 to get a product released in April 2014...
Thanks, MichaelD50!