Will also happen if you have missed B,C & D checks? I Have just gone from CI +81 to CI -37.
Checks (A&B's) should be automated, for Newly brought/leased and/or Used, visa versa!
The lack of this feature, will cost me (and no dought many others) millions!
Keep on top of your checks, may not be a problem now. But will be as you expand! As a new a/c arrives (with no routes) put A&B checks on it regardless.
Should have too do so, (should be automated) hence, why we do.
Hope that helps, for your future expansion. anyway!