the moment it stops working for me, it gets tossed.
sometimes this is after 3 shaves, 2 passes or even 1/2 thru a pass.
for 10-25 scents, I'm not going to try and make a blade work on my face.
I've had blades go south on me after 2 shaves. I've also used a blade for more than 100 shaves with no problems.
It is all relative and there is no way to tell in advance how long a blade will last, only when it misbehaves will you know when it is time for it to go