Every once in a while, I like to shake things up a bit.
Peelable hinges were used for years before the modern day hingeless mounts such as Showgard, Scott, etc came into being. Prices for early US stamps distinguish between mint never hinged and hinged copies.
Here's an interesting thought. All self-adhesive stamps have a backing paper. There is the stamp, some adhesive material, and finally the backing paper. So if you hinge your mint self-adhesive stamp on the backing paper to your album, is your stamp considered mint never hinged or not? Technically, the hinge is on the backing paper and not on the stamp or adhesive material itself. Maybe we'll establish a market for mint never hinged and hinged backing paper?
The grading of stamps takes into consideration several factors and not just the centering of the stamp (although centering is one of the most important factors). With self-adhesive stamps, will the grading consider the backing paper too? How about the registration of the inks used to print the design on the backing paper? What if the backing paper has a smudge, fingerprint, or some other minor blemish?
Collecting used setenant issues isn't easy any more. When the USPS issued setenant stamps with water activated gum and perforations, it was possible to take a block or strip of stamps, keep them attached, and use them on a package or letter. You had postally used setenant copies.
With the introduction of self-adhesive stamps, this isn't possible. The stamps are die cut so they separate completely from one another. Let's say you managed to remove the stamps from the backing paper and use them up on a package. You carefully line them up exactly so that it looks like a solid block/strip of stamps. If you soak these stamps off of the paper, the stamps would fall apart and you're left with used single stamps again.
The only way to collect used setenant self-adhesive issues is to leave them on the paper that they came on. That can be a problem in years to come because most paper is not acid free. The paper may start to damage the stamps someday. Maybe you could take a picture of the stamps together as a block while they are still on paper. Then soak them off into singles. Then mount the picture with the stamps to prove they were once joined together?
I don't know too many collectors who collect used setenant blocks and strips of modern self-adhesive issues. Now you know why. I think eventually, collecting used blocks and strips of setenant stamps is going to go by the wayside like Zip and Mail Early blocks since the USPS stopped printing those inscriptions in the selvedge of postage stamps.
The same logic applies to collecting used plate number singles. I know a few collectors who save these kinds of stamps. Now that the plate numbers are separated completely from the stamp, it takes some skill to line up those tiny pieces of paper next to the stamp. Used plate number singles on cover of modern self-adhesive stamps are going to be very rare. Whether or not there will ever be a market for them remains to be seen. If demand is low, prices will be low. Maybe used on cover plate number singles of self-adhesive stamps will be the next collecting fad?
Years ago, ordinary people used to go into the local post office and say, "Give me the stamps with the pretty picture on them." That meant commemorative stamps. Now people go into the local post office and say, "Give me the stamps I don't have to lick."
Post offices used to stock at least some of the recent commemorative stamps. Today, post offices tend to stock just the common definitive stamps in self-adhesive form (typically a flag stamp of some sort). During the transition years of the 1990s, commemoratives were still largely water activated gum (you had to lick them). But the public was more interested in self-adhesive stamps that they didn't have to lick and taste the gum. Had commemorative stamps been introduced in self-adhesive format as quickly as definitive stamps, the public may still be asking for "pretty stamps". Instead, the public got into the habit of asking for self-adhesive stamps (because you had to lick the pretty stamps) and that has continued ever since.
Another factor is convenience. Commemorative stamps typically come in a large format. First class definitive stamps are issued in booklet format. The booklets fold up nicely and fit easily into a purse or wallet. The average consumer can have stamps at hand any time they need one.
As a dealer, you would think I get a lot of commemorative stamps on my mail. I don't. About 20% of my mail is franked with modern commemoratives. About 10% of my mail is meters. About 60% of my mail is the Flag stamp (or whatever definitive is in current mass production). The last 10% is usually older stamps being bought and used as discount postage.
Postally used commemorative self-adhesive stamps are going to be hard to find on cover someday. It may take years for collectors to realize this. I wonder what the prices for these covers will bring someday?