In 2003, Technical Readout: Project Phoenix was published that postulated upgrades and newer versions for most of the "Unseen" 'Mechs from the in-game year 3067 forthwith. Dubbed Reseen, these evolutions were sufficiently visually different from their parent designs that they could be depicted. Technical Readout: 3055 Upgrade continued with "Phoenix" upgrades for the remaining "Unseen" 'Mechs, and the "Reseen" Samurai first appeared in AeroTech 2 Revised Edition and then in Technical Readout: 3039.
To wit, the "Reseen" did not replace the "Unseen" variants, or retcon them out. They are new, additional designs with new art, meant to gradually replace the "Unseen" as the timeline progresses.
The term "Reseen" is also applied to designs that were "Unseen" at one point, but were taken off the list again.