The Ultimate Model Paint Conversion Chart

I came across this interactive paint conversion chart which is really handy IMHO.

http://www.paint4models.com/

I use that site. it can be quite confusing at times :S

example:
i wanted to convert tamiya XF5 flat green with revell acrylic, it said: leaf green. i bought it and its totally off. too dark for an interior green shade!
thankfully i randomly picked out fern green and its very close to a cockpit green shade and im using that

I cant understand why you get the same colour in TWO shades?
example: there are two XF5's, both in different green shades/RGB.
WHYS THIS? and which is the correct one?
Why are there 5 revell lufthansa blues?? :S