Hi MrStrong,
i had a customer with a similar problem and there are a few variables. microsoft have changed how licensing is done since you had that implemented.
key things are:
1. are the computers on licensing or are they OEM licenses that came with the machine.
2. if they are licensing has the original supplier put the licences on your account or his but still licensing you. not to worry if thy are on his and h doesnt play ball as you can have them switched back.
Here: http://www.microsoft.com/licensing/default.aspx
There you can find all the info on licensing from basic to advanced.
there is no real simple answer for your situation without knowing which way you are covered. just because the machine has an OEM sticker doesnt mean it isnt on licensing.
If you can find out from the previous supplier if they used the licenses from the machines or whether they bought volume licenses i can assist you further on here.
failing all of the above there is a telephone number to microsoft licensing you can call (i dont have it to hand right now) whom i have spoken with a few times to solve similar situations for my customers. Microsoft seem to be very keen to ensure licenses are in the end users account with resellers and support companies as admin to them rather than the other way around. seems the logical way to me but obviously some not so upfront people can do it the other way around.
please do note though that you are NOT required to have a reseller or consultant on your licensing as this is just an option so they can assist more efficiently. i personally only have 1 client that has it with me because they have no idea about licensing.
So to summarise:
i would contact the previous supplier and see if it is OEM or licensing. if it is all OEM you should be fine as long as the labels are with all of the machines and the OS matches that label
If it is licensing ask them what your authorisation code is and more importantly what email address it is assigned to.
Shout back the results, obviously not the auth code or email address just what the situation is after speaking with them and i can further advise on how to solve your issue if possible
My Fee's? £00 but would appreciate any Kudo's