Both will tell you the
rule against topping off applies to systems with 50 pounds or over and
a 35% annual leak.

Not exactly, it depends on the type of system. The EPA Leak Repair
Summary Page says that Commercial refrigeration & Industrial process
refrigeration systems (50 lbs. & Over) have to be repaired if the annual
leak rate is 35% or more.
Comfort cooling appliances & all other appliances (50lbs. & over) must
be repaired if the annual leak rate is 15% or more.

Check it out yourself: http://www.epa.gov/ozone/title6/608/leak.html