Hello Dave,
Parts suppliers use the week number and year to indicate the date parts were made. Example HW: 52/03 for the last week of 2003. In this example the part should be found installed on a 2004 or 2005 model year car manufactured in 2004 calendar year.
I'm also thinking that HW could be referencing hardware built date and SW for software release date.
IMO the BCM (Hardware) is the same. The only difference is the way they are programmed or reprogrammed, for example power operated or fixed spoiler, Auto or Manual Transmission, Fog lights or not DRL and other difference between Base, Limited and SRT and regulations in different parts of the world..
I hope all is well with you and the XF.