A hack series must contain more than two published ROM hacks that are canonically part of the same series which have both been worked on by the original author(s). This can include spin-offs, sequels, prequels, remakes or demos.
There are many stand-alone hacks that have sequels planned by the original author(s); in the instance of these stand-alone hacks, they will need at least two published instalments to be considered part of a hack series- multiple planned sequels isn't enough for a stand-alone hack to become a series.
