New design patents have a term of 15 years from patent issuance — that is a 1 year bump from the 14 year term familiar to many patent attorneys. The straight 14-year term took hold in 1982. In the years leading up to 1982, most design patents also had a 14 year term, but applicants had the option of instead obtaining a term of 7 years or 3½ years at a lower fee. In 1980, all design patents had an application fee of $20, and the issuance fee was $10, $20, or $30, depending upon whether the applicant wanted 3½, 7, or 14 years of patent term. In 1930, the prices were $10, $15, and $20.
The chart below is a bit hard to read, but it basically shows the percentage of design patents associated with each of the three potential patent terms. The basic result is that in the 1910s, folks were obtaining all three sizes at roughly equivalent rates; By 1940, the short 3½ year term had become most popular; Then, by the 1970s the overwhelming majority of applicants were paying the extra $10 for 14 years.
This is part of a larger project that I’m working through on design patents, and I’ll be able to fill-in the gaps of the chart at a later date. I’m downloading the TIFF images for these patents; running through OCR software and then parsing that text output. It is a bit of a process, and I probably need a multithreaded approach. 
The original design patent Act of 1840 included a 7 year term. I believe it was the the 1861 Act that added the spread term, and included a respective cost of $10, $15, and $30 with an optional seven additional years.
Source: https://patentlyo.com/patent/2021/09/design-patent-3%c2%bd.html
