Unless the attorneys where you work have some legal objection why cannot you still use these checks? We handle checks out of order all the time. Boss will take a stack so he can file evictions and maybe does not use them all that day. You will know when the statement comes in the mail what checks actually cleared and as long as you enter the correct check numbers in QB to match what prints or is handwritten...
To answer your question, if you wish to physically void the checks you do that and write VOID on them and then hang onto them for 3-7 years depending on other hold requirements for records. But in the non-attorney world if, for example, a check is damaged in the printer or gets wet we do not VOID we just SHRED. And we don't keep track of it.
I do understand that law offices deal with trust and escrow and each check has to be accounted for. To account for the checks you decide not to use (myself I would just use them anytime I needed a single check) you will hav eto enter a bogus entry, save, and then VOID it. Use the memo field to show if it is physically in hand or in the shredder.
