Old Stamps On Envelopes

I have a cache of old, (early 1900s) letter envelopes (not FDCs) with stamps affixed and cancelled. Which would be more valuable, keeping the envelopes intact, or removing the stamps to add to my collection? any opinion greatly appreciated.

Letters intact.... In all probability they are most likely extremely common stamps, and you will lose value (which probably won't be much, sadly) by removing them from cover.

Why not post up aa few examples, anyway so we can better advise you, though.

The general rule is keep them on cover (if you have the space to do so). There are people who study not only the stamps, but the postmarks and postal markings that would value these much more than just for the stamp alone.

Bottom line is that you can always decide to remove them from the cover later on should you want to do so, but you can never put them back onto a cover once they are removed, so leave them intact until there is a valid reason to do otherwise.

yeah, what they said.

For stamps from the 1900-1920s often had attractive machine cancels. Also there was some experimentation with hand cancels as well. It is the cancellations and other postal markings which can increase the value of a used envelope with stamp.

Ahem (clears throat), you can do whatever you like. However, if you take them off cover, I will be forced to assault you with a soggy lettuce leaf!

Keep them on covers, see how SG catalogue evaluates some used covers of Idian states

While I don't understand those images I would suggest that you might leave them on cover so then they will retain all their postal history and markings and whatnot.

Six reasons to leave the stamps on covers
1. Most U.S. pre-1920 have a modest premium for on cover.
2. Some covers for uncommon rate payments (such as a solo 19 cent presidential paying correct rate) which increase their value.
3. Some are more valuable on cover for intended use (such as the 8 cent second bureau paying registry).
4. Cover may have historic value due to significance of sender or receipient.
5. Cover may have a rare or uncommon cancel.
6. It is much easier to remove the stamp later than it is to put it back on. If research shows that there is no value in leaving it on cover then it, at the owners discretion, can be removed.

Edit: typos.