I have gone through the process you are describing a few months ago and am
now past the "retain last Version" date.   Which leaves me quite puzzled.  I
did not set my new value to zero though, I used 2.  It matches my DB backup
count.
I still have some non API stuff hanging around and am now under the believe
that there are also other things happening.  I am under the belief that the
number of versions kept is determined by the lesser of the VERSIONS DATA
EXISTS (nolimit) and RETAIN EXTRA VERSIONS (42) .  I am trying to meet the
requirement of saving 42 days worth of backups.
Thanks Again
Matt