In all the cases where 5ppm ammonia is dropping to zero ppm in 12 hours and nitrite is dropping to just a small amount in 12 hours and the fishless cycle has already proceeded for a month or more, the people who have understocked as a first introduction have had no problems that I've seen.
The few cases that I remember where we've seen problems seemed to be where people thought they were seeing double zeros for long enough but their total Days were less than a month or there were other cases where people were still seeing traces but then fully or over-stocked and these two types of scenerios we saw problems with large spikes.
Twinkle's case and the others described just don't sound like the types that will have problems. I have no explanation for why some filters will just exhibit this "sticking problem" (which we've described many times before) and most others will do the usual think of taking a while and then dropping to double zeros and never tracing again.
WD