Keeping track of employees isn't an issue. Everybody has some number they use or are small enough not to have run into issues with just using a name.

It's when you're talking about something that sticks with a person for their entire life. A prime example is credit scores. That's something that stays with you no matter how many times you change jobs, change names, change addresses, get married, etc... Federal taxes are another area where it's important to match the name with the correct record every single time.