The story
Copyright infringement
NTDEC produced a large number of unlicensed video game copies between 1989 and 1991, which were sold in Asia and in the United States via mail order. Unusual among counterfeit cartridge manufacturers, they're often identifiable through the company logo on it and the in-game copyright notice modified to read "NTDEC", as well as the rear label featuring a green "QUALITY GUARANTY" [sic] stripe.
Nintendo of America, Inc. v. NTDEC
Two NTDEC employees were arrested in 1991 for the company's activities distributing cartridges in the US, and legal action was brought against the company by Nintendo shortly after for copyright infringement, as well as its use of the "Nintendo" trademark in its company name.
Nintendo's legal action of 1991 concluded in 1993 with Nintendo being awarded $24,059,062 plus attorneys fees of $108,829.00 and costs of $709.80, and a worldwide permanent injunction preventing NTDEC from infringing Nintendo's intellectual property rights. At this point the company ceased operations under the NTDEC name.
Original games
Between 1991 and 1993, NTDEC developed and published a number of original games in Asia, some of which were distributed in parts of South America and Europe. Many of these were credited to Mega Soft, a California-based company which was listed in Nintendo of America, Inc. v. NTDEC as their North American distribution arm. Six games previously released by them in 1991 were compiled on the Caltron 6 in 1 multicart in 1992, which was distributed in the United States - since this cartridge contains only NTDEC/Mega Soft games and carries the same CN-xx ID as the previous original NTDEC games; Caltron (or Caltron Ind. Inc.) is believed to be the same company as NTDEC.
Unreleased titles
Dragon Palace Adventure
The Pearl Turn
Caltron 9 in 1
From Wikipedia’s article on NTDEC, shared under CC BY-SA 4.0.3