aka, List Column not appearing in Managed Propperty Selector.
I am not sure if I have blogged about this before, but I do recall falling for this stumbling block earlier. If I have blogged it, then this is a worthy reminder
When wanting to map a crawled property as a managed property, please be cautious when declaring the managed property to select the appropriate type, because when you click that "Add Mapping" button to select the crawled properties to map to, the crawled properties that are going to be displayed are filtered by type you declared.
Also note columns declared as Number in a list are of type Decimal and not Integer.
Cross-posted from tariqayad.com