I've got to thank Julian Scott-Foxwell for some very useful perspectives to add to this article.
He says "I think it also worth mentioning that lifejackets can be numbered so that crews on joining can, as part of the safety brief, try on and size straps to fit. Thereafter they can pick up their own personalised LJ when needed."
And here's another point that I seem to have missed: "It should also be made clear that when LJs are wetted with salt water they should be washed down with fresh before drying and storage."
Thanks Julian, and I hope you have a very pleasant sailing season.

Its also worth pointing out that the straps must be TIGHT and the crotch strap worn to be properly effective. The lifejacket itself must be either of BS EN 396, BS EN 399, CEN 150 standard, or a DOT (UK) approved type and must not depend solely on oral inflation for their buoyancy, otherwise it's only a buoyancy aid.

Also worth pointing out that in the UK the following applies to (pleasure) vessels over 13.7 metres are obliged to comply with the Merchant Shipping (Life-Saving Appliances for ships other than ships of Classes III to VI (A)) Regulations 1999.Class XII in these Regulations.

Worth bearing in mind should some or their family try to claim against your insurance after an accident...

W.