As someone who lived through Y2K not using 4 digits for year just makes me itchy. The rest would be fantastic for a large multi building setup like Mayo.
But you can represent up to 999 lab techs with only 1 more digit. Or 946 lab techs with just 2 alpha numeric characters. Heck just 2 letters gets you 676 combinations. About 17,000 combos with 3 letters and more than 40,000 if you use 3 alphanumeric characters.