Any certain years you're looking at? Like Yoda said 2013 till now is a bunch of small improvements every few years. I wouldn't buy anything older than the 2014. This is what I remember and was backed up with some cursory googling.
2013 (black and white) - Introduced the push button bar length change/ flip flop floaters
2014 (blue and blue) - Switched the center line bar bushing to a two screw configuration, and the center line swivel updated to screws over pins securing it (if the 2013 didn't already) Improved the buttons on the flip flop floaters so it's easier to do on the fly.
2015 (blue and yellow green) - There was an inline switch to a lighter center line split after their initial release. https://www.wetestkites.com/wp-content/ ... og_Bar.png
2016 (blue and red) - Same as 2016
2017 (blue and teal) - Different flagging line stopper (might have been a 2016 change, can't remember) https://en.kitefuntarifa.com/blog/image ... system.jpg
2018 (white and dark blue) - First year that they started offering the different length chickenloops outside of the wakebar, also a different leash attachment "ring"
2019 (blue and orange) Haven't really caught up on 2019 gear but I believe this one is the first that you can swap between 4 and 5 line setup on the beach.
And for lengths of bars in relation to line length this sums it up for all years (minus the wake bar, and the race trust bar they made in 2013)
"The Trust bar is a dual adjustable length bar that comes in two options, 42/49cm and a 46/53cm length. On the smaller bar you can choose between 19 or 22m lines and on the longer bar you can choose between 24 and 27m lines"