ComplexURI.py

import falcon

class TestResponse():
	def on_get(self, req, resp):
		resp.body = "Success"
		resp.content_type = falcon.MEDIA_TEXT

application = falcon.API()
# http://localhost/item/19/01/01/Item-190101-59559ee7-e661-43c8-9da1-0ab83b9e0d8e.json
application.add_route("/item/{y:int}/{m:int}/{d:int}/Item-{yymmdd:int}-{item_id:uuid}.json", TestResponse())
application.add_route("/item2/{y:int(2)}/{m:int(2)}/{d:int(2)}/Item-{yymmdd:int(6)}-{item_id:uuid}.json", TestResponse())

Thanks for reporting!
Although this was "sort of known" for Falcon developers, I filed this as a new issue: falconry/falcon#1567
Even if we cannot afford fixing this soon, we should at least clearer document the current limitations.