New venting for handrails
The closure bend holes are to allow the last bits of air and zinc trapped in the handrail to escape. The locations of these holes will vary with the angle that the handrail is hung at. Further compounding this, the angle at which the handrail is hung, varies with its length and configuration. It is easier to understand the phenomenon of trapped air and zinc in a hollow section by using the example of a common transparent plastic bottle.
Hole location: If you fill 2/3's of a transparent plastic bottle with water, you will have an air bubble and a volume of water, clearly visible inside the bottle. By gently tipping the bottle over at different angles, you will easily see that the air bubble moves inside the bottle. Conversely, the trapped water will move too. The same thing happens in a handrail.
Length: A general rule of thumb is the longer the handrail, then the shallower the angle it will be hung at. (an extreme example to explain this would be hanging a 1m handrail and a 8m handrail - the 1m rail could almost be hung vertically in the bath, whilst the longer 8m rail would not be able to fit in vertically and so would need to be hung at an angle.)
Configuration of handrail: Just to throw the proverbial into the works, if you have a right angle bend in your handrail and the leg length is over 1m, most galvanizers will hang the handrail horizontally - this means all your vent holes are going to be in the wrong plane.
Simply, the best way to drill the holes in the correct spots on closure bends is to drill the holes when the handrail is hung up on the galvanizing header. Hartway has added some notes to their handrail venting design drawing to help prevent this problem of multiple holes. Handrail drawing.