There is no artificial limit on the number of tag changes that can be packed into a single MQTT message. The only limit that I’m aware of is the 256MB limit on MQTT message size (as defined in the MQTT spec). MQTT Transmission will pack all of the tag changes that occur within the Tag Pacing Period into a single message.
Also, if you can let me know which video mentions the 500 tag change constraint, I can look into correcting it. Thanks.