This is a good history question.
People bring it up periodically, but need to look beyond the baseline, no slighting to anyone.
King of Diamonds (GTB, 1967)
If you want to know more, look up the words, Retro Pinball LLC.
You could also request to discuss with Herb Silvers directly based on his experience and craftsmanship.
Understand the story between the considerations of the original EM and what was created with the update, how it was completed, development even in original not the "remake". It was reverse engineering in purest form. Gottlieb supported him fully, once the wrinkles get ironed out, but the market went sour in 2006, and there were still technical production problems.
HINT: Another explanation of the difficulties of creating a successful pinball company, 10 years before the present potential failures of companies such as ZW, DP, and HP, and others in the future in less than the same amount of time. It happens for reasons that could be researched.
Retro Pinball LLC is another amazing story like IPB, and would make an incredible article or updated podcast.
TNA maybe "retro" in concept, but has NO direct relation to an EM, as it is relates to SS games from the mid 80s like Cybernaut, Beat the Clock, and Lady Luck. Even Breakshot has more in common with EMs in terms of design from 1996.
Look to the past for the knowledge.