He was injured in week commencing 5/3/07 when his position was 568, 3months later (11/6/07) it was 671, gives an average of 620. If they use the 'week' before, actually 28/5/07, when his ranking 667, gives an average of 618. Not sure exactly which they would apply, either way it'll be about 618-620.
Verkerk was injured in July 2004 and his attempt at return (Napoli Challenger) in March 2006 ended in his retirement, so I think that this tournament was deemed not to count as his first tournament back, as he was still injured. His next attempt was September 2006 (Tarragona Challenger) when he was did not retire. It looks as if the 'clock' started from then.
Only doubt I have is that I haven't been able to work out where his protected ranking was used.