The Voynich Manuscript mentioned by Sherlock is real. Purchased by book dealer Wilfrid Voynich (and subsequently named after him) the mysterious book has been carbon-dated to the early 1400s though its original author and meaning remain unknown. It's also partially intact, with dozens of pages missing, perhaps the reason the remaining 240 pages have thus far proven impossible to decode. As of 2019 it's housed by Yale University's rare book library.
Detective Bell shouldn't have acted surprised at Sherlock's announcement that the bullet casing he found at the hospital was reused. As a police officer, Bell would have spent a lot of time at the shooting range, where reloaded ammunition is used very frequently since it is far cheaper than using brand new factory made ammunition.