The interior cockpit of Kovin's ship was a reuse of the cockpit from the Timeship Aeon, which appears in Future's End (1996)/Future's End: Part II (1996).
In one of the flashback scenes, Kovin's assistant is armed with a rifle reused from Waking Moments (1998).
Neelix does not appear in this episode.
In the opening shot of Voyager orbiting a planet while testing a weapon provided by Kovin, the visible part of the planet is obviously a version of earth, with North America clearly visible including Hudson bay, Lake Winnipeg, the Great Lakes, the Atlantic seacoast, and Cuba. Florida is missing and the upper Great Lakes appear to be slightly modified. This resemblance is never mentioned. Cf. "Miri" from ST:TOS, which also features a planet looking exactly like earth, and where this resemblance is explicitly mentioned in the opening of the show, but is neither explained nor plays any role in the plot.
This takes place in 2374.