Just checked through some notes on the set that are from the mid 90s-identified are around 200 different examples that have a slight change from the original card. Be it a partial S or E or a ' or a , or a ; instead of a , or 2 ll instead of a u or a large , instead of a small , or no O or CREF instead of CREE and the list goes on and on. The Wiltse & Lundgren examples are also identified. Also there are some background changes not just captions...
I would think the scene/background differences are more interesting than the caption or letter changes.
Try this-buy 10 to 20 examples of the same card. Lay them out next to each other and see a variation come to life. Also look at Nat'l from every card.
The reason some are valuable and others are not is because the valuable ones were noticed and checklisted by collectors 50 plus years ago. If this Lundgren was noted and checklisted it probably would bring the same coin as Murray, Sharp and Snodgrass. They are really only valuable because collectors are willing to pay for them.
Just last year we noticed the different color green on the Sovereign 350/460 cards. These are not any more valuable than the other Sovereigns but definately a different color. This set is endless-the longer you collect it th emore you will notice.