Indian Head Cents In Full Red

It would seem to defy logic, yet, they exist, and we know this because we can still find them.

Air-tight safes and bank vaults come to mind, as well as old collectors who stored their coins in cotton-lined envelopes inside cabinets/trays, some of which were under glass and rarely saw light, as well as being in a relatively stable environment. It helps to remember that numismatics was the "rich man's hobby" at the time and doubtless many collectors with the means to do so would have had good (by 1890's standards) storage setups.

Other means of storing coins, such as mason jars (which were occasionally even vacuum-sealed) and glass containers with lids, would have also preserved the color. Unless they were stored in the sunlight or otherwise exposed to the air, they can be buried underground and look the same way they did 100+ years ago when dug up (cf. Saddle Ridge hoard, and that was in tinned iron cans!!)

And yet, top-grade 65,66 or better RD slabbed Indians continue to bring fantastic prices. Check Heritage or Snow's website.

I suspect someone has invented time travel and goes back in time to acquire coins in full red color.
OR China has finally figured out how to make our old Copper coins again.
OR many were just put away somewhere safe.

Yes lacquer was the standard preservation method back in the 18th and early 19th century. It didn't hurt the coin and was easily removed if needed (I suspect wax would have been used sometimes as well.) The one thing you had to worry about with lacquer was the lacquer chipping or cracking. If not noticed the areas exposed by the chips or cracks would suffer differential toning.