The bishop may also be trying to figure out other things with his request to you, and not just how to enroll in seminary. We all know of "active" children or youth, not yet baptized, but over the age of 9, and without a membership record. These children or youth might be just as active as every other child in your primary or youth classes, but for various reasons, baptism may not be an option, yet. These children/youth names don't show in the usual places, so "out-of-sight" is truly "out-of-mind" for the bishop and ward council leaders and teachers who could be watching over them and leading them toward baptism.
Seminary is just one area that not having a MRN may effect. These children or youth COULD be added locally into your ward MLS system, as a "non-member," (a temporary record held only in your ward.) Doing so could solve some of the issues, such as allowing them to show up on class rolls, be called in MLS to some positions, show in directories printed in MLS (not LDS.org,) etc. Of course, consult your leaders and the parents!
"A soft answer turneth away wrath" works great on LDSTech forum boards!