Several possibilities should be explored:
- Use PlaymoDB and search by theme. For example if you know the set contains a fire truck, you could browse the sets in the category "Rescue".
- Any number embossed on a part you've got from the set is useful. This can be a year or a mold number, in no way is this a part number. A year gives you an indication of the year of the set (this year or later). Some mold numbers have been encoded on this website and on PlaymoDB. You can try to use it as a key for search engine.
- Figures from the set can give an indication about the year in which it was released (see question «How to date Playmobil® figures?»).
- Playmobil® website contains an Archives section where sets are sorted by year.
- There is a book, sold by Playmobil® (which can sometimes also be found second-hand) which gives all sets year by year. It is called Playmobil® Collector. The third edition includes sets from 1974 to 2009.