Identifying Vintage Barbie

This is a hard subject to understand and even harder to explain.  My good friend a doll dealer and I were talking and I asked her why she didn't sell a lot of Barbies.  She said to identify most Barbies would make you crazy. 
I collected vintage Barbie for many years. I did not buy them new, but at garage sales, thrift stores etc.  I did buy a lot of later special editions new until I realized the beautifully gowned and styled dolls were sewn to the box.  When you take her out of the box she looks not much better than a regular Barbie.  No wonder they tell you they are  only valuable if never removed from box.  Well I am a doll collector, not a box collector.
No, I do not have a #1, 2 or 3.  The oldest Barbie I have is from as best as I can tell is about 1968 - 1970. A Mexico manufactured doll. Most of my collection is  up to 1985.  I do have the 1962 issue of Midge and Alan.  But they are other people.  There are a few Barbies that have distinctive faces  and the originals only made a few years such as Malibu Barbie.
Well you say You have several old ones with the year 1966 .  There are billions with that date.  1966 is the year that body was patented.  The year dates on Barbie have nothing to do with the date of issue. 
It took me lots of time to identify my collection, both Barbie and her clothes.  Over the years I purchased many books and I studied them and I was able to identify an issue range of the dolls.  I looked at many pictures and was able to identify the vintage clothes.  I will go into the clothes later. 
If the vintage did not have a specific face and limited years of issue, the only way to know the age was country the doll was manufactured in.
The following will tell you the years Barbie was made in that country.
1958 - 1971   Japan.  If you Barbie has Japan that means she is 62  to 49 years old in 2020.    Sometimes there are clues to be more specific.  That is where the Barbie identification books are needed.
1968 - 1970.        Mexico
1970 - 1982.        Hong Kong
1972 - 1 978.       Korea
1974 - 1987.        Taiwan
1978 - 1988.        Philippines
1986 -  present     China
1992 -  present     IndonesiaMattel also has a facility Malaysia.