I can see your point, but the most important thing if for each story to carry sufficient verisimilitude for the readers of that particular story. The continuity serves the story, not the other way around. So all of those references to the passage of time tend to compress the further away from them that we move–which is how, in the 1990s, the original Gwen Stacy Clone story was said to have taken place “Five Years Ago.” And today, the amount of time between the first Clone story and the second one in the 90s would likely be less time than that.
But that’s all fine, as it’s incredibly rare that all of this is spelled out in this manner in the individual stories themselves. So it’s only the really hardcore and long-time fans like you and I that worry about this stuff.