AB-OSV Lifeboat requirements

I am working on getting my AB-OSV. I work in the GOM currently on a Lift boat. All my other experience is on crewboats and supply vessels. The current AB onboard my lift boat did not have to take a lifeboat course for his AB 2 years ago. Its stamped on his MMD “valid only on vessels without lifeboats” or something along those lines. Everything I am reading though says lifeboat is required for any AB. Can someone clear up the confusion for me? Thanks.