What some developers do, is make older versions free.
For example, when they release the newest v0.7, the old v0.6 (or even older, like v0.5) version is released to the public.
There may be bug fix versions inbetween (like v0.5.1 and v0.5.2), but those are only released to Patrons. When such a bug-fix version is released, there is no public release to go with it. So public version will usually have few bugs (because it will include the fixes found earlier, so it's actually the 0.5.2 version), but is always behind, with less content and less features.
Some developers reserve this public version for $1 Patrons.