The main problem is that those websites have an outdated concept of how OUIs work. Manufacturer prefixes are not always 24 bits long – they used to be in the past, but now IEEE offers both 28-bit and 36-bit prefixes (for a reduced price).
So when you see a 24-bit prefix that is allocated to IEEE itself, that means it's the "base" from which IEEE assigns those longer prefixes. For example,
40-ED-98-3 is assigned to Knox and
40-ED-98-7 is assigned to Vaisala Oyj.
You'll find the real assignments beginning with
40-ED-98 in the OUI-28 (MA-M) registry. There are three vendor prefix registries:
with a web-based search page here (select "All MAC (MA-L, MA-M, MA-S)" as the database).
(It's a very similar situation as with IPv4 "classful" addresses – everyone used to get the same size block, and it turned out that there are not enough possible 'prefixes', and at the same time many manufacturers really need a much smaller block than is offered. So the solution was to designate a block of longer prefixes.)