Following a question by AILA members on CPT and OPT, this is what the USCIS answered:
Some Designated School Officials (DSOs) endorse Forms I-20 with only the dates of practical training, and not the employer name. May an employer accept such an I-20 (with the passport and I-94 card) for I-9 purposes without additional documentation, or must the employer obtain documentation listing the specific employer?
An acceptable Form I-20 for curricular practical training or optional practical training STEM extension (STEM OPT) should have all Employment Authorization fields completed. The Form I-20 Employment Authorization fields include: employment status, employment type, start and end date of employment, and the employer’s name and
An acceptable Form I-20 for 12-month optional practical training (OPT) is not required to have all Employment Authorization fields completed but should indicate OPT recommendation or OPT approval. A foreign student in F-1 nonimmigrant status participating in OPT must receive Form I-766, Employment Authorization Document (EAD), from USCIS before he or she is authorized to work. He or she may not begin OPT until the date indicated on the EAD.