Thanks for your thoughts and the long write up.
As noted in my earlier post, I had considered getting the display data directly from the database table. For your reference, the timestamp will be ok in seconds

sudo-code
#ie:
#Read and save serial number to database.
#Table: | prefix | number | stamp | (index the stamp)

#Now build for the display... 

"SELECT DISTINCT number FROM table ORDER BY stamp LIMIT 20"
etc;

## Now get prefixes associated with those numbers.
## Remember the other serial numbers (prefixes) may be received at any
+ time in the past.
for (each number) {
  "SELECT prefix FROM table WHERE number=$_"
  fetch() 1 to 4 elements per number {
    ## build, in a string, array, or hash for display
    "number XX XX XX XX"
  }
}
[download]

And that looks like a nightmare. :)

update
Tanktalus, don't spend any more time on this. There's more to the script than I've outlined, like some of this runs in a forked child process and data is LWP'd to another script, etc.

Your earlier solutions will serve my needs and I sincerely thank you.