Sternbach and Okuda were really clever in inventing the "signal drops from FTL to lightspeed at set distance" thing, as it explains every instance of commlag in Star Trek just fine, as long as we choose the placement of the nearest booster relay right.
What it doesn't explain, as pointed out above, is the surprising
lack of delay at the very long distances of "Where No One Has Gone Before". Less than a century for a million-lightyear call? But the inability to communicate FTL across such distances is back in VOY, and in fact seems to hold true for every other piece of Trek besides "WNOHGB". So we might do well to note that the evidence from that one episode is far from unambiguous.
LaForge: "Message on this has been transmitted to Starfleet, Sir."
Data: "Which, traveling subspace, they should receive in fifty-one years, ten months, nine weeks, sixteen days-"
Picard: "Mister Data!"
Apparently, everybody thinks it's realistic to send a message, as they indeed proceed with sending it. But Data is the only one who seems to think it would reach home in mere 51 years; nobody agrees with him there. And Data appears to be having some internal disagreement on the issue as well: first he says 51 years, then 10 months, then 9 weeks, then 16 days. But it makes no sense to say that the message will travel for 51 yrs + 10 months + 9 weeks + 16 days, because 9 weeks is more than a month and 16 days is more than a week! Thus, grammatically Data is offering at least three and possibly four
different estimates for the delay - all of them in the conditional case of "should".
It would be pretty simple to say, then, that Data's conditional is never gonna materialize.
If the message traveled in subspace, then it might arrive after one of the three or four suggested time intervals, depending on other parameters Data is not allowed to dwell upon (possibly because Picard thinks they will just remind everybody how hopeless their situation is). But the message probably will
not travel in subspace, and will only reach Starfleet after millions of years, and may be lost in the background noise anyway. What LaForge sent was not a call for help, but a self-obituary.
Timo Saloniemi