I've just realized that you edited your code. Here is another one below to reflect the change:

on !*:join:#:{
  msg # $read(wc.txt)
}
on !*:part:#:{
  msg # $read(part.txt)
}
raw 821:*:{
  msg $1 $read(wcback.txt)
}
on !*:quit:{
  var %q = 1, %m
  while ($comchan($nick,%q)) {
    msg $v1 $read(quit.txt)
    inc %q
  }
}

The ! prefixed in front of those events will tell mIRC not to send the message to channel when the client that runs the code parts, joins, or quits. (yourself)

The ! tells mIRC to send message when other people do so only.