Progress tracker step 5a and 5b

I am working on a project that involves multiple screens and forms. There are approximately 15 screens the user will go through to complete a registration. Due to technical reasons dev team want to label one screen as 5a (driver license info) and the second as 5b (address info), user then moves to screen 6. Is it ok from a UX stand point to label multiple steps as 5a, 5b or should it just 5 and 6? thanks