MongoDb updating old documents

I am new to MongoDb and to the NoSQL concept of storing information. Unlike in SQL Server, adding or updating a column name in a table will affect all of the records. I can assume that when I pull a record, that column will be there. It may or may not have a value depending on how it was setup.

But how would you handle a situation in MongoDb where you have an outdated document and you want to pull it and now your code is looking for a property that did not exist or was just recently renamed?