It had been originally intended to have the SEA ratified by the end of 1986 so that it would come into force on 1 January 1987 and 11 of the then 12 member states of the EEC had ratified the treaty by that date.
Algselt oli ette nähtud, et akt ratifitseeritakse 1986. aasta lõpuks, et see saaks jõustuda juba 1987. aasta 1. jaanuaril ning 12 liikmesriigist 11 suutsid selle selleks ajaks ka ratifitseerida.