E-way bill from vehicle no.

Part B includes the vehicle number, and where Part B is not filled, the EWB can be said to be invalid. So indirectly it has been made mandatory. Some concessions like transport within 50 kms need not file Part B is given. 

Extract of provisions:

Rule 138 - Explanation 2.- The e-way bill shall not be valid for movement of goods by road unless the information in Part-B of FORM GST EWB-01 has been furnished except in the case of movements covered under the third proviso to sub-rule (3) and the proviso to sub-rule (5).

It can be said to be invalid Vishesh. Although, we can litigate based on S126.