Crappie take several months to develop eggs, starting in late Summer ... but, when & how fast they develop depends a lot on their geographical location (& the subsequent prevailing conditions of the waters in that location).
Unless the water temps do not change drastically throughout the year, I doubt a Fall spawn would survive ... if in fact they do "actually" spawn in the Fall. The fry & their food source can't survive very low water temps.
Many people "thought" that Crappie were spawning in the Fall ... simply because they were finding egg sacs in them. But, even if the eggs were developed enough to lay in the Fall ... the milt production of the males may not be, which would lead to a "false spawn" or (at best) an "attempted" one. If the males don't make beds & wait on the females to come, there would be little chance of a viable spawn.
... cp