You can select/deselect certain frequencies in the any of the search system in above listing. all maybe to search all even though you have deselected some. ALL (pressing F2) will likely search only those still selected.
While I have listened to the above-mentioned searches, I was hesitant to use the Service Search FrL/O (F1) button because I didn't know how to Un-Lockout the frequencies. And because no frequencies were being selected/deselected "all/ALL" made no difference.
Taking your reply as a starting point I found in practice it appears "all" scans only the selected frequencies, while "ALL" scans every frequency (selected and deselected). Therefore, in "ALL" mode I not only scan every frequency, but having PAUSED the scan I can step through the channels to find the Locked-Out channel(s) and un-Lock them. In "all" mode the Locked-Out channels are invisible, the scanner just skips over the deselected channel.
Thank you for your reply. It has increased the utility of this scanner for me.