Reading previous period value is logic

Hi,

There's a need to read previous period value is logic for some processing, can you please help me out how this can be achieved. I have a selection for time in the package called %TIME_DIM% and I am running for the current period. I have tried following options

First

*WHEN XYZ
*IS "ABC"
*REC = (FACTOR=GET(TIME=PRIOR), SOMEDIM=VALUE)
*ENDWHEN

When above code executed with current period (no record exists for current period) nothing is read.

Second

*XDIMMEBERSET TIME = PRIOR, %TIME_DIM%
*WHEN XYZ
*IS "ABC"
*REC = (FACTOR=GET(TIME=PRIOR), SOMEDIM=VALUE)
*ENDWHEN

In the above case no record is selected and surprisingly the select statement fired (got it form the log) is for the last time period maintained in the system - 1. So if I have time dimension members till 2020.DEC this picks up 2020.NOV. I didn't understand why?

Would appreciate help on this.

Thanks