The 2391 was split up into two qualifications the 2394 and 2395 (presumably as a money making exercise and to confuse everyone, oh sorry I meant to make it clearer which areas are covered in the exams!)
If you want to do both initial verification and periodic inspections then you should do both exams (which would be a good idea from a knowledge point of view, even if you only want to one or the other).
Doing periodic inspections is complex and demanding and would really require you to know a lot about initial verification before moving on to periodic.
If you were just doing initial verification then the periodic one would be fairly irrelevant but can often be seen as half of the 2391.