The documentation is correct. Since you can only have one T0 per edge:
"An Edge node can support only one tier-0 gateway or logical router."
If you need more scale than you will need more NSX instances.
Thanks for your input but the documents of NSX previous versions 2.3 or ealier NOT latest 2.4 says:
"An NSX Edge cluster can back multiple tier-0 logical routers. Tier-0 routers support the BGP dynamic routing protocol and ECMP."
That is very weird and is it the degraded feature?
The statements are actually different. You can have only 1 Tier-0 per edge, and this is confirmed on page 49 of the Reference Design guide that came before 2.4 and is available on https://communities.vmware.com/docs/DOC-37591 Since Edge Clusters are made of multiple Edge Nodes you can have multiple Tier-0 routers on them, just not more than 1 on each individual edge.