Keep it Relevant
All content is on a path towards obsolescence. This is especially true with SOPs as they are on a constant path of becoming irrelevant. Slight changes to tools, videos depicting former employees, even new paint or labels on an item says to your user, “this SOP is old”.
Maintaining your SOPs and keeping them current is just as important as writing them in the first place. Best practices say you should have both formal and informal processes.
Formal Maintenance Process
Building a formal review and maintenance process is the best way to keep SOPs current. Usually, the team that wrote the SOPs are best for this, but you may want to insert new people for a fresh perspective. Having a team maintain your SOPs divides up the workload, making this easier for everyone.
Then prioritize your SOPs. Safety SOPs usually go to the top of the priority list and often justify very frequent review. SOPs related to regulations are also towards the top of the list, along with SOPs that have wide or frequent use. Next, set a schedule and stick to it. Many businesses tie performance bonuses to such activities, which is fine. Buying lunch for the team works in many circumstances.
Informal Maintenance Process
You should encourage all users of your SOP to provide feedback. Put a prominent message in your SOP along with an email link that goes to all the team members. Those inbound changes should go through a triage process with the team. Decide if they are urgent enough to fix outside your formal schedule, or if they can be queued for the formal maintenance process.
Regardless, you'll want to take user feedback very seriously. Be sure to acknowledge the feedback and clearly communicate how you intend to resolve the suggestion. A reward system might also be a good idea.
Don't ignore the small things. Perception really matters and even slightly out of date SOPs will have a marked drop in usage.
It's a lot to do! Perhaps you should create an SOP for updating your SOPs!