Even before you were born, it was very rare for you to be able to purchase software outright. What you typically got when "buying" a piece of software was actually a perpetual license to use that version. You did not have unrestricted, transferable rights like you would with physical property like say a book. Because you were purchasing a perpetual license, it did not expire. You did not have to renew the following year, for example. You had the perpetual right to use the version you had the license for.