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My question is maybe simplistic but in regard to the 1993 Welfare Souvenir Sheet and all others for that matter he has the full souvenir sheet on one side where it's intended to be placed and on the opposite back left side he has hinged a block without the surrounding sheet. Is this common practice?
I'm not quite sure I understand how this looks. Are you stating that there are stamps hinged to the back of a souvenir sheet or that the stamps are hinged to the back-side of the page (essentially a page not intended for any stamps)?
If hinged together, separate them. The risk of them sticking together is too great. If hinged to the back of the page, leave them alone.
For selling purposes, here's a quick break-down of what you can expect when selling these.
Federal republic of Germany (West Germany) from 1949 through roughly 1960 can have some significant values for both mint and used. Never hinged prices go through the roof on some of the higher face values.
After 1960, the stamps are common and are of little value. The expectation of catalogue values is that if mint, they MUST be never hinged. If used, hinged has no relevance. Mint/hinged stamps from this era sell for a pittance - I would estimate as little as .05/ea regardless of face value. Thus, there's no reason to worry about the modern souvenir sheets and extra stamps. Just count them with the rest.
DDR (East Germany) is even worse. I frequently buy collections for as little as .01/stamp. 1949 to roughly 1955 has a few nice values (especally used), but after 1955 has little to no value.
Modern Germany with Euro face values (€) should sell at 50%-75% of face (using 1-1 ratio of € to $) regardless of being hinged or not.
I would recommend selling the modern albums as-is. Count the total number of stamps and mention that in your auction listing.
I hope this helps. Good luck!