That's good question. I can't answer it definitively and would like to know the answer, but I can say:
a) a lot of varieties of celery are 'self-blanching' which means unlike traditional varieties, they don't need to be earthed up or enclosed.
b) I grew both types last year without earthing up either and there wasn't much difference between the two - the original variety (Granada F1) was perhaps a little firmer.
PS They get unhappy if they don't get enough water.