  A disjoint $(v,k,k-1)$ difference family in an additive group $G$ is a
partition of $G\setminus\{0\}$ into sets of size $k$ whose lists of differences
cover, altogether, every non-zero element of $G$ exactly $k-1$ times. The main
purpose of this paper is to get the literature on this topic in order, since
some authors seem to be unaware of each other's work. We show, for instance,
that a couple of heavy constructions recently presented as new, had been given
in several equivalent forms over the last forty years. We also show that they
can be quickly derived from a general nearring theory result which probably
passed unnoticed by design theorists and that we restate and reprove in terms
of differences. We exploit this result to get an infinite class of disjoint
$(v,k,k-1)$ difference families coming from the Fibonacci sequence. Finally, we
will prove that if all prime factors of $v$ are congruent to 1 modulo $k$, then
there exists a disjoint $(v,k,k-1)$ difference family in every group, even
non-abelian, of order $v$.
