Your examples indicate that a slot for a number can be specified as:
I need to request dates.
I know Alexa has a slot type that accepts a wide variety of date references and returns a possibly-incomplete ISO datestamp, and that there some helper libraries (AmazonDateParser) which will expand those into ranges with fully resolved start/end date.
But I’m not sure how to specify that Alexa type in the inputs:  section, and I’m not certain what the Dialogflow equivalent is.
Is there a doc page which shows the standard declarations/handling for various types? (If not, there problem should be.)
Or is there an example which shows how to ask for dates?
(Answering my other question: Amazon now has an ordinal slot type, in beta test. I don’t know whether it’s clever enough to handle numbers expressed as “Twenty nineteen”, but since their dates do, one can hope.)