Patents filed before Oct. 1, 1989, fell under the old patent act, which gave companies 17 years of protection from the date the patent was issued. The new act provides 20 years of exclusivity from the date of application.
Monsanto wasn’t issued the patent stemming from the March 28, 1987, application until April 26, 2005, which means under the rules of the old act, it doesn’t expire until April 26, 2022.
Before this latest patent, Monsanto’s herbicide tolerant technology had been protected by a bevy of other patents. The latest one protects all of its Roundup Ready canola products from potential competition from other glyphosate-resistant canolas.
There isn't just one patent and that is probably where the confusion comes from.