Are stamps that are printed on envelopes collectible? Meaning they are not a separate stamp that you affix to the envelope, but you buy the envelope with it printed on.
Yes they are, some cut them out and collect like that but I would advise to keep the envelope intact. If you have a look round ebay you will find them on sale and that will help to give you a idea of what you have
I also think those are collectible and agree with Steve that better if those stamps are left attached to the covers.
Saw this cover with printed stamp online, cover from Santa Claus. http://t3.gstatic.com/images?q=tbn:ANd9GcTPGigXwceQFurYv4yHJUDGu5CZ5CEk708rA8MQ_FbGvdDO75jzVA
Lots of unused covers with nice printed stamps. http://media.liveauctiongroup.net/i/8444/9797911_2.jpg?v=8CD198B040DCDB0
No, I'm sorry I don't. I received bulk mailings in the past in envelopes like these, but since I wasn't into stamps then, I didn't keep any.
A cover with printed stamps that are canceled. http://3.bp.blogspot.com/-zFnL42gfKJo/TxqqdKCfZlI/AAAAAAAAA44/yWSvEuYPkyk/s1600/PPA.jpg