What happens when a non-creature receives "+1/+1 until end of turn" effects, then later becomes a creature?

Question

A recent question, Can Disallow prevent me from crewing a vehicle?, brought up the following scenario: Veteran Motorist is tapped to crew a vehicle, but the crew ability is countered by Disallow. The vehicle remains a non-creature with no power or toughness (301.7b). However, Veteran Motorist will try to give it +1/+1:

Whenever Veteran Motorist crews a Vehicle, that Vehicle gets +1/+1 until end of turn.

This ability does get triggered, even if the ability was countered, because Veteran Motorist was tapped to pay a crew cost:

702.121b A creature “crews a Vehicle” when it’s tapped to pay the cost to activate a Vehicle’s crew ability.

What happens to this "+1/+1 until end of turn" effect? If I successfully make this vehicle a creature later this same turn, will it have a +1/+1 boost, or will that have disappeared somehow and not apply?

Let's suppose I have another untapped creature around and I'm going to use it to crew the vehicle, or I have Ensoul Artifact or Tezzeret's Touch or Tezzeret the Schemer's emblem ability available to use.

Answer 1

Thinking about it in a regular usage scenario, doesn't the vehicle get the +1/+1 effect before becoming a creature?

When you tap the Veteran to crew, isn't the stack:

1. Vehicle gets +1/+1
2. Vehicle becomes a creature.

So, the vehicle gets +1/+1 before becoming a creature, but the effect applies after becoming a creature. In fact, there's never a point in time where it is a creature without the +1/+1.

Answer 2

In the example case you brought, the animated vehicle will still have the +1/+1, however this is honestly the edge case for +1/+1 effects since Veteran Motorist specifically gives the buff to the vehicle being crewed.

Most +1/+1 effects specify they effect creatures, which means the card needs to be a creature when the effect resolves to get the boost in the first place. Ampryn Tactician for example buffs all creatures when he enters. Veteran Motorist is in fact the only until end of turn buff I can think of that specifically affects a non creature permanent this way.