Shimano Mega 9 speed and Dyna System 10 speed Issues

I guess nothing is free in life. As I was converting my 1995 Team Marin from 8 speed to 9 speed for my son, I learned that you cannot use the Shimano XT RD-M773 Dyna rear derailleur with a 9 speed shifter (XT, XTR, LX or SLX). RD-M772 and RD-M773 look very close and similar but looks can be very deceiving. The dyna 10 speed front derailleur is not a big issue but the dyna rear derailleur will not work with the mega 9 speed as it stops around 6th gear and does not advance anymore. Hopefully you guys don't make the same mistake. Similarly if you have 10 speed dyna shifter, it will not work with RD-M772 as the shifter requires RD-773 (or 10 speed dyna rear derailleur). If you have questions please ask and hopefully I can help or direct you to the right information highway.