As far as I know, most compostable plastic is only compostable in a digester. It behaves like any other plastic in a landfill.

Regardless of the service availability, it's so complicated to determine what can be recycled/composted in an area that the vast majority of material ends up in the landfill stream. The only solution my employer has found is to have a team go through all the trash after each event to sort it into the correct streams. That, plus using durable vessels that get cleaned between events, allows a venue to have minimal landfill output. We only have one client that is willing to commit to that level of effort and cost.