Dear Valentina,
If you have defined a object or model reference only for one model type, then only the models of the specified model type will be shown. Thus, you need to define a reference for each model type.
Example: Only for model type “Practice”:
1OBJREF
2 mt:"Practice"
3 c:"B"
4 max:100
Example: For model type “Practice” and “Sample”:
1OBJREF
2 mt:"Practice"
3 c:"B"
4 max:100
5OBJREF
6 mt:"Sample"
7 c:"A"
8 max:100