FD on valve servers

On valve servers u can choke for 6 ticks, so FD shouldnt work as intended (and its seen on visuals as FD marker flickering), but i saw some people who FD nicely and marker dont flick. How can it be explained? And also, is this thing untrusted (I kinda understand why yes but not sure)?

it depends, you need to choke 2 cmds minimum for desync , some users use a bind to disable the desync to gain more available cmds duck more and no fake duck is not untrusted for that small usercmds