Indeed it may be possibile. What are the possibilities though? Likely? Unlikely?
Do they usually do it? There are indeed many sonnets- about eight.
edit: also another question: do you need to mention the number of the sonnet when quoting from the sonnet?
I would say it's unlikely (I'm hoping they'll be lenient). Usually, they don't specify.
I don't actually know Browning's poetry, but if it's unclear which text you're quoting from then yeah, I suppose you should mention the number.
If you're writing a pragraph about say sonnet no. 1 though, and you put in a quote from it, I don't think you should write the number.