Hi Andy and welcome to Just Answer.
My name is Cher and I will do my best to answer your question.
I've been researching this for you for quite a while and there is not much information out there. I did find a site that has your model number, 5211, but it is not a 52 HP. Here is the page from that site: http://www.tractordata.com/farm-tractors/001/6/8/1688-zetor-5211.html
If you scroll all the way down, you can see that it says serial numbers for this model are unknown, but the manufacture dates for this model were 1985-1992. I checked this site as well, and it also has no serial number.
You can contact this person to try to get more information, perhaps on the 52 HP of this model, and the year this serial number was manufactured: [email protected]
This is their homepage: http://www.zetor.com/
Here is general information about tractor serial numbers, which explains that different parts of the tractor have different serial numbers:http://www.tractordata.com/articles/technical/serialnumbers.html
You might try posting on this zetorworld forum, to find the year of your serial number:http://www.zetorworld.com/cgi-bin/x-forum.cgi?show=topic&page=1&topic=3344
I realize I wasn't able to actually supply the information you requested, but I tried to give you as much information as possible with websites/emails to try. You are not obligated to rate this answer or leave feedback if you are not satisfied, but please do not rate negatively, just do not rate at all or let me know if you would like me try to research further.