First generation anticoagulants kills rodents over the same time period as 2nd generation anticoagulants.
A rat or mouse may feed on any anticoagulant bait over 100 times before it dies.
One feeding does not exist!
Poor and insufficient placement of bait stations can be mistaken for resistance.
Norway rats from Chicago have a 100% mortality rate with 0.025% warfarin found in Kaput Warfarin Products.
21st century warfarin is a much purer form than that used for earlier testing. It no longer has the metabolies that are distasteful.