"James R. Kirk" is not an example of bad forethought in WNMHGB, since that was the first episode written with that character. Nor is Delta Vega an example of bad forethought. By the way, the author was Samuel A. Peeples.
The "James R Kirk" issue is really irrelevant, and that can be excused as a "growing pain". I also didn't say it was "bad forethought," I said the writer didn't know what he was doing insofar as TOS "history" is concerned (irrespective of *who* the author is).
The "Delta Vega" point is different than Kirk's name, however. It establishes a location for the action -- which is near "where no man has gone before." To later suggest DV is right next door to Vulcan is bad planning. I could have believed it was some largely uninhabited planet near Vulcan (name withheld), or a moon of Vulcan, but the chosen route was just bad writing.
Lastly, why isn't Scotty the least bit concerned that Vulcan was destroyed, if "Delta Vega" is within earshot of the planet?