I am not 100% sure of this but as far as I know you can be certified by ASNT by three forms:
- ACCP
- SNT-TC-1a
- CP-189
SNT-TC-1a and CP-189 are both employer based, so a NDT Level III signs the certificate and a representative from the company (General Manager, NDT Supervisor, or so). The test is made by the employer or some level III asigned by the company, according to their written practice and the certificate remains valid till the NDT Tech leaves the company. It doesn't have registration on the ASNT but the employer must have a database with all the certificate numbers. You can obtain Level II through ASNT you do both exams in ASNT, but practical exam depends of your current employer, this certifies the individual, independent if he changes of employer.
ACCP is different because the test is made in the ASNT, not in the company so this one certifies the individual also.
Hope it helps!