I use a standard number system but am changing it to better identify more info on the job.  I use:

YEARMONTH(clearance test done)-RCO#-(adding this next section)MAC#-ADDRESSNUMBER

for example if we remediated at 12322 Main Street and achieved clearance on 1/5/2021 and the Mold Assessment Consultant was John Q with license number MAC1111 then my certificate number would be:

202101-1206-1111-12322