It could still be both. We already saw in Enterprise technology used that could penetrate Romulan and Suliban cloaks (albeit not the cloak used on the Bird of Prey). If such sensor technology became part of the standard set of sensors on ships in the mid-22nd century, and there were no major jumps in cloaking technology for the next century, then the idea of a successful invisibility cloak would be alarmingly new by the mid-23rd century.
Yes, exactly my thinking. If the technology was moribund for over a century until a new method was devised, then its revival could come as a surprise.
Anyway, what Spock actually says is, "Invisibility is theoretically possible, Captain, with selective bending of light. But the power cost is enormous. They may have solved that problem." So I'm sorry, King Daniel
, but you're dead wrong when you say that "The idea
of an invisible starship was new" at the time. Spock was fully aware of the idea, familiar enough with it that he knew not only how it could potentially be done, but what the practical impediments were. Which suggests that Starfleet did have prior knowledge of experimentation with invisibility.