Pre War Card Blank Back vs Non Blank Back NOVICE Question
 

I know there any many factors at play here: year, set, player, rarity, etc., but in general if you have the exact same card front, in the exact same condition/grade, say a Shoeless Joe 1916 Sporting News Back and the exact same front but a blank back, how much less value is the blank back card. And actually could be any player just using the above as an example. I'm more memorabilia, and a card novice. Just a general idea of value Blank Back vs Card Issue Back.

different sets...
 

There are many different sets that have different backs and the same fronts. Each has their own values and scarcity levels. In the T216 series there are 5 different backs. Each one has their own scarcity and value level. On M101-4/5 it is the same scenario. Blank backs of those are generally worth a bit less than most of the ad backs. Some ad backs carry a higher premium than others. It really depends on the specific set and ad on the back.

With your example of a Joe Jackson M101-4/5 having a blank back vs having a very rare back, you could be looking at multiples of value more for a really rare ad back...ie Holmes to Homes, Everybody's, Mall Theater etc....