Man, I actually did work on the Census in 2000. I'm trying to remember now..
ID - I was given a "generic" ID from the Cenus Burea. IIRC, it did NOT have a picture on it. I remember it looked pretty cheezy and I think it was essentially just a business card type card with a place to type or write my name. I don't have it anymore, but I can't recall if I turned it in or just lost it.
What did I do - You have to remember that 90% of the Census is done by mail. The forms are mailed out and most are returned. The only time anyone comes to your door is when forms are not returned from a specific address or the Census has a reason to want to canvas a particluar neighborhood.
For me, my job was to take a list of addresses in a certain area and then physically drive to each location and leave a Census form in a plastic bag on their door. These were addresses that either did not return forms or were believed to have been missed in the mailing for some reason. (New construction, etc)
I wasn't actually supposed to ring the bell or have any contact with the people, just leave the forms. I was told to ID myself if asked. I wasn't to take any completed forms, just tell them to mail them in if they asked.
I also had to stick a label on each form I dropped off and record the very long number on each label on the master list of addresses I had next to that address. None of this was computerized. It was a paper form and we used these crappy little low-bid government pencils to write the really long series of numbers on the form. I was amazed at how low tech and buecratic the whole operation was.
I had a supervisor who "ran" four or five people at my level. He'd been hired in and trained a few months ealier than I had. He'd meet us at a local diner where we'd turn in our completed lists and get new assignments. Usually he'd meet us one at a time as we completed assignments, about once a week or so.
My understanding was that the next step was to be several weeks/months later with live Census takers knocking on the doors of the people who still didn't return a Census form even after we left one hanging on a bag on their doorknob. I wasn't involved in that as I'd found a real job by then and quit the Census. (We were all basically hired as temporary workers and paid by the hour).
As far as keeping forms, it wouldn't be hard to keep a few, especially if they were either blank forms or generic forms with no info filled in. They may have tracked the forms for the next step more closely, I don't know. I did wind up with probably 200 of those plastic bags marked "US Census 2000" that we used to hang on doors. I used 'em as trash bags for my car for quite awhile before I ran out. (Wished I would have saved one or two now, but at the time I was sick of them).
EDIT: A quick Google search says the 2000 compliance rate was 73% overall. I would have thought it was higher than that.
Here's a couple good articles
http://www.nytimes.com/2000/05/30/n...lack-of-worker-id-s.html?ref=walterlmccaffrey
http://www.censusdiscriminationlaws...-action-case-introduction&catid=16:front-page