20 years in what direction? If earlier:
If later (2005) then you're saying TKD still much resembled Shotokan in 1985 and had not yet come into its own as a unique system. I'll leave it to the TKD experts here to debate this point.
As I said, the main point was not the timeline, but the line of significant divergence from its ancestor. Again, this is subjective. I am aware that TKD has been changing in recent decades as it searches for its own identity and will say it's no longer just a variant of Shotokan but its own unique style, as separate from Japanese karate as that is from Okinawan karate.