I've said over and over again: Logically, there would be an ongoing arms race between cloak and sensor technologies, so there would not be just one kind of cloaking device, there would be many different ones coming and going. And canon itself gave us indisputable proof of this long, long before ENT came along. In "Balance of Terror," the cloak was detectable by motion sensors, but by "The Enterprise Incident," the Romulans had a cloak that couldn't be detected that way. In ST III, the Klingons had a cloak that created a visual distortion, but they'd overcome that problem by ST VI. In said movie, they had a cloak that surmounted that problem and
allowed a ship to fire while cloaked, but Spock devised a way to track it. Yet by the TNG era, Starfleet couldn't
track cloaked ships and it was again necessary to decloak in order to fire -- so clearly it's a totally different technology by that point, a replacement cloak that got around Spock's detection technique at the cost of undoing the fire-while-cloaked advantage. And we've seen later instances where means of detecting cloaks were devised, and yet in later episodes we were still seeing cloaks that couldn't be detected.
So it should be indisputable, both from common-sense reasoning and abundant canonical evidence, that cloaking technologies are constantly being rendered obsolete by new detection technologies and then replaced by new cloaking technologies devised to foil those detection technologies. So there's no continuity error here. Or rather, the discontinuities that exist actually help make things more plausible, because they accidentally create evidence of the kind of back-and-forth race between stealth and detection that logically should