How long will this edition last

A couple of years ago, I purchased an Adobe Photoshop Elements from COSTCO.  And I used it with success. About a year ago I was informed that I could not use it because it was purchased from an illegal source.  Why would a purchase from COSTCO be illegal. I was able to use the edition until a new one came out. How do I know this will not become illegal when the next "improved" edition appears.  Is this a way for Adobe to make money, by not supporting the past editions and you can only use the new editions?