Dive shops may still recommend annual overhaul regardless of current manufacturer policies. As labor and material costs have increased, many regulator manufacturers have adopted the every 2 years or 100 dives recommended service period. Some experienced divers do not service their regulator until it exhibits signs of wear (typically an unstable first stage IP or a dribbling second stage), which means their regulators often go for many years between overhauls. Thus the answer is that service frequency seems to be more a matter of opinion and experience than science and research.