Why?
Even 5 years ago I might have agreed, but it just keeps getting easier and easier. You don't even need to be artistic anymore to attempt to create 4-packs. You need resources, an eye for detail, and zero concern for the idea of right vs. wrong (at least in regards to fake 4-packs).
Honestly, I believe the biggest challenge would be cutting the cards after printing. I think everything else would be pretty easy. Plus you could sell a couple of test 4-packs, just to make sure nobody is instantly calling out your work or noticing something.
I don't have the energy to go back to those most recent SC 4-packs, but I stared to wonder about the other figures inside those 4-packs. We've often said how 4-pack cases often had very similar figures in all of the packs. As I remember it (not taking the time to look back) the only consistency was the SC. The rest of the figures were pretty diversified. I don't remember seeing a lot of any other one figure. Just a thought.
Why?
Difference in materials. Cardboard, plastic, ink, glue. No matter how good you are at faking something, 100% of the materials WILL be different than the original used. Even if they're all virtually identical or really close... even if ALL but one are perfect... They're still 27 year old materials put together on old school, analog equipment from the 80s. Plus, Inkjet printing is easy, but it's different than silkscreen printing. Something would have changed, no matter what. There would be a way to tell them apart. If they're wasn't, whoever is making them, should spend his time making $20 bills instead of wasting his evil genius on buying, repackaging & reselling M.U.S.C.L.E. figures on FeePay.
I've worked in a few dozen different factories over the years. Making stuff, packaging stuff. Packing stuff up & putting it on pallets. From Shipping & receiving to manufacturing. I've even worked in the stores putting the same crap I used to make on the shelves. It's amazing how many materials and little steps go into making something as simple as a pack of M.U.S.C.L.E.s. Getting each of the dozens of steps & materials 100% perfect is pretty much impossible... Especially with quarter century old materials & equipment involved...
You never know though. There always could be a psycho Puerto Rican reseal bandit on the loose... buying up mint Satan Crosses and resealing back in to perfect packages with common M.U.S.C.L.E.s that can fool even the most serious collectors. A true engineering mastermind... hiding away in his evil little M.U.S.C.L.E. lab... surrounded by big ass computers...
or...
maybe someone just found a kick-ass case or two hidden in the back of a shipping container or from the back of a back of an old warehouse... and the guy is full of shit. His idea of being a "20 year reseal expert" is using a hot glue gun to patch up the crap he buys at the Puerto Rican swap-meet.
If the recent packs ARE fakes though, it would be interesting as hell to see them up against a real one... If they can whip out perfect 4 packs without a hitch, molding up perfect Satan Crosses & Super Rares should be about as hard as making cookies.