Why we cannot see the Variable Tags in Expression field of Trend Tag forms in Vijeo Citect. However we can see the Variables Created as Local Variables.
The problem you are facing is because of the number of items in Variable Tag is greater than the Max Listed item parameter defined in Citect Project editor.
To see these tag in trend configuration you will have to do the following:
1. Go to Citect Project Editor--> Tools--> Options and increase the parameter Maximum List Box Items to 10000.
2. Open Citect Computer Setup Editor and add the parameter [CtEdit]MaxHelpRec=10000.
3. Pack and Compile your project.
4. Close the Citect Explorer and startup again.
After restart you can see the tags in Trend Configuration.