SETVALUE

The SETVALUE function adds a value to a GTS or override an existing value. If the tick already exists, this function will overwrite the first one it encounters in the GTS. If the tick does not exist, it is appended. The ADDVALUE function adds a value to a GTS but do not override an existing value.

The SETVALUE function only works on GTS, not on lists of GTS like those generated by the use of FETCH. If you want to use SETVALUE after a FETCH, you will need to extract the GTS from the list, using GET for instance.