I don't think there is any such limitation. Certain trains in the past having 4-5 rakes, had only 2 LHB rakes and other ICF rakes and bookings were proper that time. A recent example I remember is HWH ADI Express, whose 2 LHB rakes were in use and other 3 or 2 ICF rakes.
Moreover, TATA CDO also has rakes, 3 rakes of TATA JAT have been freed as it has got LHB rakes. Don't know why they cancelled the decision.