I was an early tubeless rim person on my MTB. Those Stan's Arch EX are extremely difficult to pop the bead over.... never looked forward to tubeless maintenance, removing the giant latex booger before the start of the season, and trying to pop the bead over.... the only thing that worked was the Crank Brothers Speedier lever. The LBS broke a lot of plastic levers getting the tire beads to pop over.On my MTB, the fluid inside the tire starts to dry up and lose its effectiveness after 6-12 months. This isn't easily apparent through visual inspection, but if you wait too long you'll find out when you get a puncture that doesn't seal.
This article says 2-7 months, but mine lasts longer than that. However, even if you can hear it sloshing around, it doesn't mean it's still effective.
How Often Should I Replace the Sealant in Tubeless Mountain Bike Tires? - Cycle Baron
Short answer: As an avid mountain bike enthusiast, I've certainly had my share of tubeless tire difficulties over the years. To compound this frustrationcyclebaron.com
And also, Stan's standard sealant has its limitations for puncture hole sizes... for punctures expected that the standard stan's won't seal, they make a "Race" sealant