No problem. It can be confusing. The "W" just signifies that it has Windows keys.
Not just that. The AT-101W was made for Dell by Silitek. The AT-101 was by Alps for a bunch of different companies including SGI and Dell. They look somewhat similar but are different internally.
Oh, to add to the confusion, I think Silitek also made an AT-101 which was similar to their later AT-101W but without Windows keys. Just in case you thought there was an easy pattern going on here.