Some bulbs just split more rapidly than others, but most will multiply over the years and form a clump. The more there are, the less nutrients and space there is for each individual bulb and they start to struggle. You can push dirt out of the way but a neighboring bulb will push back, and often times a crowded clump will have bulbs pushed up out of the ground because of the lack of space.

Was that what you were wondering about?

Thanks Katob. Yeah, just short of offsets hanging too close and clumping, when one says bulbs just split/naturalize, spread, I just could not picture clumps breaking apart and doing some couple of ~inches~ of movement in soil,