I can confidently say in my research that the ports were Nice Code-developed, though that isn't easy to prove in short terms. Some examples off the top of my head:
*Numerous NOAC ports of Atari 2600 games (including Activision/Imagic titles) exist as Nice Code-hacked versions, but were never officially released on any licensed plug & play. This includes Street Racer ("Lightning"), No Escape ("Ice Ocean"), Pressure Cooker ("Candy Workshop"), and quite a few others.
*Nice Code released hacked up versions of unreleased "revisions" of the Intellivision ports. For example, the Snafu hack "Shrew Mouse" has three players, while the official INTV plug & play only shows two. It would be incredibly difficult for such features to be hacked in if Nice Code didn't, at the very least, hold the original source code.
*Other verifiable Nice Code games are known to be included on Techno Source consoles, meaning Techno Source presumably commissioned Nice Code to make the Intellivison titles. Nice Code may have also been hired by Techno Source to produce the Activision/Imagic titles; however, Techno Source's eventual p&p under this license used emulation.
*Some of Nice Code's generic hacked versions are dated 2003/2004, meaning they would have had access to the games at effectively the same time the "licensed" consoles released. As such, it's not like they got ahold of the source code after the fact or something; the generic hacks were produced alongside the official versions.
Additionally, you seem to be confusing two entirely different plug & plays mentioned here. The Missile Command NOAC port is on a different 10-in-1 plug & play; it was released by Basic Fun in 2017 (see
https://www.youtube.com/watch?v=zIYnHzGgpig). The Techno Source Activision console, while also not NOAC-based, was released in 2005 (see
https://www.youtube.com/watch?v=zSZLbjOBojc). The Jakks Pacific versions are presumably Winbond-based.