Lights vary from batch to batch, there so many things that can make a few percent lumens difference between the same lights.
I know you probably already saw the thread but for the $73 bucks it’s well worth the money to get as close as you can and later on if you buy another tube or replace light meters you still have the lights to calibrate by. WTS: Calibration lights for DIY integrating spheres / lumen tubes - 67 € -