Years ago, collectors would ask businesses to save the envelopes from their mail for them. In some cases, businesses would agree, especially if the request came from an employee. I’m sure many business owners just rolled their eyes at such requests.
That has changed a lot over the last 20 years and especially in the last 10 years. Identity theft is a very real concern. Businesses are much more reluctant to let go of their envelopes. In many cases, businesses shred envelopes. What if someone could trace a case of identity theft back to a business that gave away their envelopes? The company could be held liable. Attorneys would have a field day.
I’m sure the public is better protected against identity theft. The cost has been that myriads of used stamps and covers that were available in the past are a thing of yesterday. Today, you would be lucky to get a business to agree to just save the stamps from the corner of the envelope for you. Few, if any, businesses would save the entire envelope with return address for you.