Voyager-A was active as of 2385, and LD takes place from 2380+. Either there's a production goof, or Janeway self-destructs the 'A' as well as it's next two successors in rapid succession. Given her propensity for initiating auto destruct, I guess it's not too far-fetched lol.
Maybe she's promoted to Fleet Captain, and gets put in charge of Voyagers A-C all at once, to take them on a deep space expedition. After they're predictably swept away in an anomaly, the D is built
Or when the shipyards found out she took command of the "A", they just started immediately building B through D assuming they'd be needed in short order lol.
I think she directly says "what's that, like 10 generations?" after noticing the -J and gets corrected that it's 11 (since she forgot about the non letter Voy)