what I know through experience is this, I have no interest in the clad Ike's, which weigh out at 22.6 gms.
I have quite a few blue (uncirc's) and brown (proofs) Ike's, the 40% silvers, all bought before the "big scare" in rolls. these are all from the SF mint. I weigh every single 90% silver coin and all 40%'ers, I mean every single coin, thousands, because WHEN I was still buying pre-65 90's and 40% Kennedys, as well as the 1971-74 blue Ikes, and the 1971-72 brown Ike's, I always bought rolls. ( early on, I stopped buying 73-74 proof Ikes, because the SF mint turned out both a clad AND a 40% proof Ike in those years, I blame Richard Nixon, because Ike couldn't stand that greasy savage beast)
anyway, I noticed something a bit peculiar when weighing 40% Ike's....and my scale is right on, but I had a variance, the weight is 24.6 gms, right?...and about half hit that mark, and half went +/- about .05 gms.......got reads from 24.0 to 25.0 gms...some guys think I might have gotten Chinese fugazi's......no, I magnetized them,glassed them, these are American made, I just believe in that era, quality control at the SF mint, really wasn't up to par.....
I forget the exact years I was buying Ike's, but if memory serves correct, it was on the downside of the $50 toz peak, and there was not a lot of interest in 40% Ikes, hence in auction, I was getting them at melt....or sometimes a slight discount. (Plus Ike was one of my favorite Presidents, during his tenure in the WH, a lot of the left thought him a dottering, not that bright old man, who just played golf,,,how wrong they were, he had a brilliant strategic mind, he had an unparrelled pen, great writer, and he was a great man, who's life was dedicated to service to Nation,and makes these pygmies today in the GOP today, look like the narcissistic chickenhawk swine they are....sorry for the rant, couldn't resist)
so again, why the variance in the weights at the SF mint, circa 71-74?....look at the time period in our history, it was a bad time, Vietnam was a disaster, Nixon was screwing around with the dollar, the national mood was dismal, we had our first real "oil shock", which included a near showdown between us and the Soviet Union over the 73 Israeli-Arab war, etc etc etc.....and I think the SF mint at that time was just poorly run, they were just going thru the motions, punching a time clock...it was happening all over the US at that time.....not as bad as now, but bad....just my opinion.
as far as "mistakes" in minting during the 90% era, are the Washington Quarter's out of the Philadelphia mint, the Type B reverse from 56 to 64. When I was buying rolls of uncirc Wash's, I didn't know about this, and when I found out, I went back to these rolls and MARONE!!!...I have a bunch, and its a numi thing, and the one's I carefully cherry picked seem to be in the MS65-67 state.....what IS a TYPE B reserve?...well it wasn't a "mistake"......here:
"TheType-B Reverse is a business strike coin that was struck using a retired reverse proof die. These variety coins are very collectable in high grades (MS-65/66/67). "
"Description of the Type-B Reverse:
Wider separation between the E and S of States, The tail feathers are sharp and well defined, The leaf at the arrow tips was strengthened and rises above the arrow tips, The leaf below the arrow shaft was strengthened and touches the arrow shaft, The overall design has more detail."
"To date no Type-B Reverse's have ever been reported minted at the Denver mint. "
"NOTE: The Type-B Reverse was NOT a mistake by the mint. The mint used left over used proof dies because they ran short on business strike dies. Used proof obverse dies were also used on business strike coins."
here's the website, that contains pictures of these numi specialties:
http://www.washingtontype-b.com/same thing with the 1964 Kennedy Proof "accented hair".....when they rushed thru the design, they let the First Lady have a say, and she thought the "hair" in the middle was a bit much, so they reworked the die for the business strike. a few years back I had the good fortune to pick up four rolls of frigging FLAWLESS 64 Kennedy Proofs, having no idea, REALLY, about the "accented hair" ...now these four rolls all look to be in the MS66-69 state, and when I went to look over them again? Holy cow!...the seller was just rushing silver out the door,and hadn't cherry picked yet, and I found 12 high MS "accented hair" types.
"why don't you slab 'em?"....naw, one, I don't want to spend the money, two, i'm not selling one toz of silver,and having to do 1099's, and all that crap.....I only buy, I never sell, and never will sell on the white market......and if you think i'm nuts?....y'know these this whole "jade" thing that's planned? (go to youtube, plenty of citizen filmed mil exercises and train loads of equipment already crossing the nation, I kid you not)...anyway, i'm sitting in my nest, middle of nowhere, watching a film my son suggested, "Chappie"...a great film, and all of sudden I hear this familiar roar getting LOUDER....it was a C-130 blasting 100 feet off the deck, down my ridge road...I was so pissed, I know what they were exercising, a nape of the earth run.....where you get low to avoid radar, to get up on the target drop...I wasn't pissed at our boys, I love 'em...i'm pissed at leadership, coz I thought this jade thing MIGHT be a bunch of hysteria designed to get the American people fearful....but now? might be the real deal, I don't know the ultimate PURPOSE, but there's too much video and first hand accounts coming in from all over the country....somethings afoot.