is
Euphorbia pseudocactus cristata

the same as
euphorbia lactea crest

this is what add plant says
Confirmation requested: It's possible that this plant already exists as Elkhorn (Euphorbia lactea 'Cristata'). Are you sure you want to create the plant?

thanks!

I can't find any information suggesting that E. pseudocactus and E. lactea are the same plant, so I'd say you should go ahead and resubmit the proposal for Cristata as a cultivar of Euphorbia pseudocactus. I could be wrong, of course, but no one else has answered your question.