Well, Q set up that Glomesh fence as a symbol to Picard that he wasn't letting them go further than "where no one (human) has gone before"
Except the mesh was
between Earth and Deneb IV, preventing Picard from reaching that planet where humans had apparently already been to.
Note that "Star Charts" has an error on page 34, where Mandel accidentally used Alpha Leonis IV for Farpoint's Deneb IV, when he meant Alpha Cygni IV. And, of course, the other Deneb is Deneb Kaitos on p 33.
Actually, the original idea behind
Star Charts was that Picard's crew would never visit any location more than a couple of hundred lightyears from Earth. Deneb IV was never supposed to be Alpha Cygni, but instead one of the numerous other Denebs (stars with the word "Leg" in their name) out there - supposedly quite close to Earth, just in a direction that nobody had bothered to explore yet. Indeed, plenty of Earth's relative vicinity would remain unexplored at the time, as we see in TOS that nobody has yet been to nearby places like Beta Geminorum in the mid-23rd century.
Humans might have been to Alpha Cygni, on trips taking years or decades, and might have brought back firsthand data on Denebian Slime Devils and the like. Or then such knowledge would only come indirectly from nonhuman travelers. But by the book's assumptions, no travel to such distant locations would take place during the actual aired episodes of TOS, TNG etc., and the maximum speed of long distance travel would indeed be an "Okudaic-Sternbachian" thousand lightyears per year.
Remember "That Which Survives?" Spock said they could get 990.7 light-years in 11.33 hours at warp 8.4.
To nitpick, what Spock says is merely that the ship is 990.7 ly distant from the stranded landing party; that they need to get to the castaways ASAP; and that Scotty thus better bring the ship to top warp speed. At some later timepoint, the dialogue establishes that staying at warp 8.4 would mean 11.33 hours of time remaining.
How much time passes between those two scenes is unknown. In simplest terms, the landing party is still alive at the second scene despite lacking water, so it can't be too many days, but there is no other sign of passage of time. All the landing party has been doing in the meantime is digging a grave for D'Amato, and carving a tombstone for him (which must have been very slow work since phasers supposedly can't penetrate the local geology...). Oh, and it looks like they haven't been through a night yet, but that's just an impression.
This still doesn't drop warp 8.4 to "manageable levels", but at least we could take it down an order of magnitude or two. And if we wanted, we could do the rest by saying that Losira displaced the
Enterprise in time as well as in space.
Timo Saloniemi