Mercury Dimes

The 1928 and 1941 has both large and small "S" varieties. The large "S" is the rarer of the two. There are some RPM'S also. nlp

The 16-D, probally goes without saying though.

Ok thank you

Both 21s

It's possible, but I wouldn't expect it. Even if you were to find one, it would be a 36 or 41-45.

In realism the chances of finding any Silver coin in rolls anywhere are almost all long gone. Way to many people do rolll searching for just Silver coins.
With Mercury dimes they are rather plantiful at almost any coin shop, coin show or flea market. Very few are ever counterfeited due to their size makeing it not really worth the trouble except the 16D.
A really decent source of info is a book called the Red Book by Whitman Publishing. You might find a cheaper version at a used book store or flea market. For Mercury dimes you don't need the latest version of that book.
Although many know of certain large and small Mint Marks, more and more are appearing all the time. As already noted the sort of famous 42/41 and 42D/41 are rather popular. They get scarce with the 21, 21D, 31d. Not a lot of books out there on Mercury dimes which is odd since it is one of the more popular coins.
I've got about 6,000+ of those things and plan on someday examining all of them for more varieties and errors. MAYBE.
Here is what a 42/41 looks like. From one of my Albums.

Be extra cautious about the 42/1 dime. I was offered to purchase a collection of Mercury dimes. The 42/1 dime was completely fraudulent -- made from chasing the silver into a 1. The date is so small that its hard to see even with a decent magnifier.