Remember that "antique" does not necessarily apply when searching for and collecting Mattel toys -- the traditional definition of antique (having to do with age for the most part) just does not apply, since the Mattel company has not really been around all that long as compared to antique toys in general. For that reason alone, we would consider their toys to just old and/or vintage and their value to based solely on the condition and availability of any particular toy in question. After all, many people have an old Mattel toys in their attic that are virtually worthless to anyone but the nostalgic owner of that toy.
Knowing this, it's a "Buyer Beware" situation in the collecting of these toys, so that is why we repeatedly remind you to do some homework before going off the deep end and paying hard earned dollars for a worthless old toy. Get informed! It's not that difficult these days, especially with the Internet. Typically we recommend library books, price guides and trade magazines, but in this case the Mattel company produced many catalogs over the years that can serve as excellent resources in classifying and valuing old Mattel toys.
Get to know the particular periods, materials and styles that pertain to old and antique Mattel toys. If this case that is not very hard, since you are dealing with such a limited period of time. Some suggestions may be: About.com's collecting club pages. You can also contact the Mattel Toy Company directly through their website and purchase a limited amount of catalog information. They can also put you in touch with local clubs in your area.
There are always local antique dealers that we have found are always happy to talk antiques and provide you with input you can use to get started. If you have a particular interest (that is a particular old Mattel toy you are seeking) many of these dealers will assist you in a search -- for a fee of course, but you may find that the fee is very reasonable and directly related to the valuse of the toy in questions.
New abbreviations for states became prominent around 1963. Between 1943 and 1963, the largest U.S. cities used "postal zones." These postal zones can date major centers, such as Houston, as being in that twenty year period (1943 to 1963). If your old Mattel toys have a postal zone number following the state in the address, it dates between 1943 and 1963.
The bar code method of pricing began use in mass commercial applications around 1975. So if your old Mattel toys boxes have bar codes on them, figure a date after 1974 and most likely after 1981.
If they were were made in Japan or China here is some more information: Old Mattel Toys marked "Made in Occupied Japan" date from the U.S. Army's years of occupation after World War II, being 1945 - 1952. More rare are old Mattel toys marked "made in Nippon". These was made in Japan between 1891 and 1921. If marked "made in Japan" it's after 1921.
Toys marked "Made in China" or "Made in the Peoples Republic of China" most commonly date after the U.S. and China Trade Agreement of 1979 and generally are not of much value.