Here's my logic:
All noms MOC given out are due to the Academy by Jan 31- known fact.
Principal nominees get the first shot of receiving the appointment once found qualified by the academy. That would be several hundred. The x number of people with LOA's and a nom will also receive appointments (LOA's are supposedly rare but based on various Facebook groups of dedicated applicants, they do not seem that rare).
Therefore, a good proportion of applicants get appointments in Jan-Feb. Despite having a nom and LOA, I am still waiting for the BFE.
As for the qualified applicants with noms, they fill in the slots after principal noms and LOA'ed people. Those probably hear back in March-April.