For what I know is not the same refrigerated than freezed, the freezeeing does damage Lantus, but as long as is refrigerated and unopened the pen should be ok until the expiration date.
Once opened I think almos everyone uses it for more than the 28 days but they keep it refrigerated, I did usually took one pen out of the fridge and I leaved it at room temperature because Babu hated when insulin was cold and I never had any problem with it , but I did usually discarded the pen after a month, Insulin down here si much less expensive than in the US, so it was not such a big deal.
For what I know the reason that the pen says do not refrigerate after opened is because the shooting mechanism (which we do not use anyway) may get damaged with the cold, not the insulin itself