If the institution provided you with a set of properties which they would be asking you to list for sale AND they gave you written permission to advertise them as "soon to be listed", I am not sure why the AREC would care. You are providing a requested service to a client.
Since the primary purpose of the AREC is to 'protect the consumer', I question who is being served if you do NOT comply with the client's request.
Besides, the statute says "advertising for sale" ... according to your statement, they were not being advertised as "for sale" but in advance of availability for sale. Of course, if someone got their hearts set on a property that the institution decided not to market, you might have a problem.