My guess would be that most Imperial citizens never bother to get a Universal ID, which is probably only necessary if one wants to travel offworld. Though an ID probably makes a lot of onworld things easier -- maybe banking with an interstellar bank, or enlisting in the Imperial military, or maybe even obtaining a marriage license (the point made above about inheritance is very interesting.)
For some lower pop or tech worlds, getting your ID might be a real bother: you've got to travel all the way to the planetary capital (that's a 200 dipthong trip!) with all the necessary documentation and then find the appropriate Imperial office and wait for days. Maybe it's an Imperial consulate, or an office of an Imperial representative. Might be a nice modest revenue line for petty nobles.
Dame Agatha, when not "overseeing" the Holbrook platinum mine from the vantage of the Luxus casino in the New Topeka Grand Hotel, also hears the petitions of Imperial citizens once a week by appointment only. Three days a week her office is open to notarize official documents and receive applications for Universal IDs, court actions, military academies, chartered universities, and other vital functions of the Third Imperium.
Maybe getting an Imperial ID is the personal equivalent, more or less, of an Imperial LIC corporate charter: essential for interstellar trade, but useful or prestigeous for others who may not strictly need it.