When trying to date or locate resources for vintage fashion, seeking out originals of the same style from actual vintage documents can be difficult. One great resource for dating 20th century fashion are the many home sewing patterns published through out the century.
The photo of Lilly Pulitzer above shows her wearing a cotton long muu muu dress with matching cotton print 'babushka' head scarf. It is a style that shows up also in sewing pattern Simplicity 6445 from 1966. The original photo is dated about 1963, so we know that any dress will probably be withing this range, especially considering how home sewing patterns can stay in print for a few years. Lilly's own style tends to not fluctuate, so it is easily possible that 1966 is a good date for a dress with this style of sleeve.
This photo of Lilly jumping from a plane is great because we can clearly see how the banding on her shift is placed along the side slit with a bow at the top. The sewing pattern Simplicity 7091 from 1966 has this same side slit silhouette. Simplicity 5455 dates from 1964, so we can see that a side slit shift is a strong look during this era.
This is a Lilly catalog illustration without a date. The patterns shown above show similar silhouette shapes and handkerchief head scarfs that were often part of Lilly's ensembles. Sewing pattern Simplicity 7529 (1968) has this look.
With the popularity of caftans during most of the 1970's, we can find quite a few caftan sewing patterns. This by Simplicity 6390 (1974) is a great example of how closely Lilly's own caftans kept this classic style during this time. We can expect her caftans to have this same look.
Locating vintage patterns can be easy to do, with Pinterest, Etsy, and Google images showing many examples to choose from. The images here come from the online site: Wikipedia, -- http://vintagepatterns.wikia.com where you will find many pattern covers archived.