Actually that isn't at all unheard of. Guide rails are extrusions and they vary a little.
That pair is maybe beyond acceptable and if you can swap one for another that is closer
in size then all the better.
Because the rails vary some the best practice when joining is to set the straight edge against
the right side (splinter guard side) of the middle spine. That is the edge the saw references.
The far outside edge is irreverent as far as the saw is concerned.