I'm not sure about simply adding people to YM - I've never had any issue with surnames there, but....
Yahoo 360° is VERY VERY BAD in this respect !! Many times I have had friends accept my invite to join my Yahoo 360, and as soon as they do my 360 shows me their full name - or even sometimes just first name and last initial - which I never knew (or wished to know) on YM itself.
Example: John Smith is on YM, as BlackPrince. I know him well on there, as BlackPrince (but never knew his real name). He signs up to 360 (just using his BlackPrince name) then VOILA!, I don't even see BlackPrince mentioned, but... a new person appears on my 360 as "John Smith" !
If/when he realises this, he CAN change the default settings in 360 so he DOES show as only BlackPrince, but by then the "damage" may be done!
SHAME on Y!360° !
