registration number vs license number

registration number and license number both are nouns.

Word	Noun	Adjective	Verb	Adverb
registration number	Yes	No	No	No
license number	Yes	No	No	No

As nouns, registration number and license number are synonyms defined as:

registration number and license number: the number on the license plate that identifies the car that bears it

registration number (noun)	license number (noun)
the number on the license plate that identifies the car that bears it	the number on the license plate that identifies the car that bears it