Spectral sequence $B^1_{p,q}= B^\infty_{p,q}$ definition, nlab

Question

In an introductory notes to spectral sequences, nlab, Definition 1.26 we define

$$B^r_{p,q} = \partial(F_{p+r-1} C_{p+q+1})$$

and

$$B^\infty_{p,q}= \partial(F_{p}C_{p+q+1})$$

So what is the difference between $B^1_{p,q}$ and $B^\infty_{p,q}$? Or any references would help!