We had a case last week, where a departing B717 was given details of class E traffic at A095. After departure, I updated the position and received the response,
"We are not showing the traffic on TCAS"
The traffic was in the jets 11 0'clock at 4 miles and was showing on the tower situation display. The 717 pilot elected to maintain a level below the traffic. As were passing the traffic, one thousand feet below the class E aircraft, TCAS finally picked up the traffic.
A similar situation occurred at Rockhampton the previous week.
These are a good reminders that TCAS is not infallible, only another tool