Certificate - noun: "A document confirming that someone has reached a certain level of achievement in a course of study or training. A university accredited certificate."
All current LEGO Serious Play certification processes, no matter which training provider, offer 'certificates of completion'.
Provided you complete the training course you get a certificate of completion, this kind of certification does not mean people who are 'certified' have met quality assured standards of practice.
However with SERIOUSWORK courses, trainees practice their facilitation skills and get feedback from peers. We'd argue that SERIOUSWORK certification is the gold standard. SERIOUSWORK Certified Facilitators have actually facilitated workshops using LEGO Serious Play during training.