The
Concordance function will only search the
Background Read-Only TM if no hits are found in the
active TM.
If the option
Search First in Background TM is checked, Concordance will first search the
Background Read-Only TM, and only if no hits are found, it will proceed with the
active TM.
What if you want hits from both active and background TM? There appears to be no provision for this; but there is a workaround.
Export your
active TM and add it to your
Background Read-Only TM. Thus, you will have matches from both.