I collect postcards of Lincoln, Nebraska and have for years...I can tell you that it is not uncommon at all for postcards to have different reverses..I have some postcards with the same front that have up to 5 different backs.....sometimes it's a result of the same manufacturer printing them in different years, and sometimes it's a different manufacturer who bought the rights to the artwork/photo or bought out a printing company.
And sometimes it's hard keeping up with the front variations.
