I'm sure there's somebody on this board who can enlighten me about this.
We see a couple of TNG characters wearing TWOK (or variant) uniforms in the past. Picard, Jack Crusher. We also see the crew of the Enterprise C wearing them in Yesterday's Enterprise, which was, what, only 22 years before the events of TNG's third season? (so only 19 years before Farpoint)
One assumes then that the TNG uniforms are relatively recent when we first see them in the TNG pilot. In Beverly's flashback sequence in Violations we see Picard wearing the season 1 TNG uniform on the day Jean-Luc brings Jack Crusher's body back to her, as do the crew of the Stargazer in The Battle. Admittedly both of these are visions brought on by outside forces, but if we take them at face value we might surmise that the new TNG uniforms were phased in during Picard's tour of duty on the Stargazer, as we do see Jack Crusher wearing the TWOK style (and we know he served on the Stargazer).
Does any source actually pin down the uniform change to a specific time? How long before TNG do we think it changed?