Public Domain Content before 1923- Can it be sold to foreign countries?

I was under the impression that any work published before 1923 in United States by an United States author is safe to sell as an information product, until I read this.

"The following is, perhaps, the most insidious trap of all. Although a work may be in the public domain in the United States, it may still be protected in other countries. For example, a work by a United States author that is PD in the United States for failure to renew, may still be protected in countries such as Germany -- where copyright duration is based on when the author died, not a specific term of years. If you plan to publish a public domain work abroad, you may be required to obtain permission if the author died within the last 70 years. If you fail to obtain permission, you will expose yourself to the risk of one or more lawsuits overseas. Beware! Many foreign works that were previously in the public domain for failure to comply with technical requirements of United States law (including copyright notice and renewal requirements) were restored to copyright in 1996 under the GATT and NAFTA international trade treaties. In order to be restored, the foreign work had to be under copyright in the "source" country, and not first published in the United States. Revived works, which are no longer in the public domain, cannot be used without permission of the copyright owner."

Now as someone selling information products, if my company is based in United States and I sell a work from an United States author online, would I be in trouble if I sell these books to foreign countries?

Please advise.

Dan