Great question. We guarantee that the pants will still work just fine after 50 washes at 40°C. (All hail mild cycles.) That's over 4 years of periods, if you have a regular flow. However, the pants can be used for much longer even though we can't absolutely guarantee the same performance after that.
What we can say is that they're totally safe to use after the 50 washes. So, wash, bleed and rewash away to your heart's content. We recommend washing your period pants before first use.