Further news! I was in the Family Records Centre at the weekend copying out Blunden marriages when I came across an entry in March 1900 for a Jessie Mary Blunden marrying in Lambeth, ref. 1d 408. Remembering that you had mentioned that your Jessie Mary Blunden took the name Blagdon upon marriage, I immediately looked up marriages under this name in the same Quarter and found an entry for a William Charles Blagdon marrying in Lambeth that had exactly the same reference!
I think that we can safely conclude therefore that my earlier guesses in favour of the Lambeth births have now been proven. Since I'm interested in tracing and tying-in Blundens where ever I find them, I'd be most interested to learn more from you about your line.