Well we don't have to worry about a young person's surcharge anymore.
I'll review W3 to see if I can find this benefit for US employees and compare to our current reservations.

Edit, added additional research:

On the IBM US Travel Homepage is says "Contract Rates may be used on business and personal rentals in the United States and Puerto Rico...." So, perhaps the separate staff benefit to which you refer is a UK thing? I can't find any other reference to personal rentals. But, at least I know it's permissible to use the corp rate for personal travel.

I just have to figure out if I need additional insurance. I found a chart which shows what insurance is provided w/corp rate for personal rentals. CDW and LDW are included, in the US (which I think includes PR), TPL, PAI, PEC, TP are not included in personal rentals.