I don't have any comparisons, but how I was able to tell that a few of my chicks were shrink-wrapped is because the membrane that was visible through the pip looked dry and papery--kind of flaky. The membrane should look moist and flexible, not papery and brittle. If it looks papery and brittle, it may be time to get in there and help your chicks out! The ones I helped out of being shrink-wrapped ended up being just fine, but they had already pipped and started zipping and just got stuck because the humidity went down for a few minutes.