First: these plants are outdoors, not in a greenhouse, so they are in sync with the season and some are starting to go dormant so their foliage is changing colour or drying back. They can still be planted at this stage, they just don't look as lush when you pick them up. 

Second: the primary issue with late fall planting is the potential for winter frost heave, which is when the crowns of plants, especially ones that have been newly planted, are worked out of the ground through repeated freeze-thaw cycles. The risk of this is highest in areas with consistently wet soils. The potential harm to the seedlings can be mitigated by spreading a mulch of leaves (4” to 8” of loose leaves) or wood chip mulch (4”-6”) over them as soon as the ground starts to freeze in the late fall.