According to this (from 2004) it's been NGA all along:

https://www.nextgov.com/people/2004/02/whats-in-a-name/21950...

Although the new title is four words long, the agency will officially use a three-letter acronym. This is by design, according to NGA officials, who feel that the new title more accurately reflects the agency's true mission, which is to provide intelligence and analysis rather than simply reproducing maps and imagery.

There is one NGIA on the Wikipedia page, in the title of a document from 2014:

https://www.governmentattic.org/11docs/NGIAoigGAMPC_2007-201...

So more like a common misspelling?