I agree with Jedi.
WE 421A was made by Tung Sol, most people seem to agree with this assessment, because WE421A looks exactly the same as Tung Sol 421A and and some Tung Sol 5998.
The only point up to debate is wether WE 421A is actually the same as TS 5998. WE 421A is a cherry-picked TS 5998, most people seem to support this from what I read. It seems WE designed the 5998/421A tube, and TS manufactured these tubes using WE's patents. When TS manufactured the tubes, the ones with better potential and can have higher transconductance would be labeled as WE 421A and shipped to WE. The rest were labeled as either TS 421A or TS/Chatham 5998.