I actually have this argument many times a year over the use of PPE for working at height. People put stickers and permanent marker on building helmets, same on harness webbing, and the effects are just unknown, they weren't designed to be drawn on and have non-approved adhesives put on them. Each manufacturer has a maximum life for a product, and it is a maximum, the first use could be the last. Petal state a harness must NOT be used more than 10 years after date of manufacture, regardless of when purchased, yet people are happy to put their lives in this ageing harness saying it is complete nonsense. Nobody has come out of an old (undamaged) harness yet, but I'd imagine on the way down, they will be thinking that they should have spent the £250 and got a new one when it was due. I tend to change mine every 5 years or so depending on how much use it has had. I've got 3 of the bloody things!