The Old King's Crown · Board game rules
Does Rally allow you to move fewer spaces than Retreat?
Quick answer
Neither Command moves cards across board "spaces" — both move cards to your Hand, but Rally is capped at a set number of cards while Retreat has no cap within its Region.
Details
Rally and Retreat are both Commands that return Active cards to a player's Hand, but they work differently and aren't about movement across the Map's spaces. Rally (Self) only lets you move the card itself to your Hand, while Rally (Any X) lets you move up to a specified number of Active cards (which may include cards from any Region) to your Hand [p.39 — Rally].
Retreat, by contrast, lets you move any number of your Active cards in that card's Region to your Hand — with no fixed cap — and additionally lets you move your Herald and any number of Supporters in that Region back to your Player Board [p.38 — Retreat].
So the real distinction is: Retreat is limited to a single Region but has no maximum number of cards (and also recovers Heralds/Supporters), whereas Rally can have a fixed maximum (the "X" value) but isn't restricted to cards in one Region.
Watch out: Don't confuse either Command with Flank, which is the Command that actually moves a card to a different, unresolved Region [p.38 — Flank]. Rally and Retreat only move cards/pieces back to your Hand or Player Board, not across the Map.