Many years ago I competed in a cadet match using "No4 Rifle as issued" sponsored by a provincial rifle association. One of my team mates won the match and was challenged by the runner up on the basis that the winner's rifle was not issue because it had a MkI rear sight. The challenger was using a "Regulated by Fulton" No4 with a Mk3 sight but definitely not as issued. The challenger was also a close relative of the official judging the match. The real winner was disqualified. I have been invited to shoot with this club many times since but I will not.
You may be a real expert but remember you are up against people who just plain KNOW!
The op does have a valid concern.