Do they vest once the design patent is granted or do they go back to some period earlier (retroactive)? I’m asking specifically about design patents.
The term of a design patent is 14 years measured from the date of grant.
The term of a utility patent on an application filed on or after June 8, 1995 is 20 years measured from the U.S. filing date; or if the application contains a specific reference to an earlier application under 35 U.S.C. 120, 121, or 365(c), 20 years from the earliest effective U.S. filing date, while the term of a design patent is 14 years measured from the date of grant (see 35 U.S.C. 173).
35 U.S. Code § 173 - Term of design patent
Patents for designs shall be granted for the term of fourteen years from the date of grant.
35 U.S. Code § 289 - Additional remedy for infringement of design patent
Whomever during the term of a patent for a design, without license of the owner, (1) applies the patented design, or any colorable imitation thereof, to any article of manufacture for the purpose of sale, or (2) sells or exposes for sale any article of manufacture to which such design or colorable imitation has been applied shall be liable to the owner to the extent of his total profit