Yes there were. These were known as Safety Coffins.
The coffins contained a string attached to a bell and usually a breathing tube that could be opened by someone buried alive.
Before modern medicine many of the ways used to confirm death were fairly subjective. Pricking someone with a pin, holding a mirror or other small shiny object under their nose to ...
For me, it feels like it's based on a few reasons. That being said, I haven't found sources for these, it's solely my analysis.
The word 'nun' is a palindrome, and a mirrored N makes it symmetric and visually appealing.
Valak is a Demon, disguised as a Nun. He is the King of Hell, and is trapped in the house of God. He is the master of ...
Maurice they show in The Conjuring is 20 years older than the one in The Nun. This movie takes place 20 years before The Conjuring where they show the case of Maurice. They also mention "20 Years Later" before playing that footage.
There is no continuity error. It is just a different actor playing an older version of a character.
BlueMoon93's answer seems spot-on, to me, particularly the part about inversion connoting subtle corruption or infestation. We see the same principle of "invert a random letter to indicate demonic stuff" happening in at least one other recent (2012) horror movie — not coincidentally, also nun-themed.
Although I can't find a proper official source, from what I found it's the effect called The Backwards R(The Backwards Я effect).
My first Analysis
TvTropes states that The Nun is the earliest film in The Conjuring series chronologically, taking place in 1952, which also confirmed by producer Peter Safran.
During the filming of ...
The key is later taken from the young nun (Victoria)'s body and used to retrieve the vial with the blood of Christ in it. The blood is then used by the main characters in the ritual to attempt to exorcise/banish the demon and seal the rift.
This is presumably what the nuns at the beginning were also planning on doing, but they were interrupted and killed ...
how the cross appeared on Frenchie's neck?
During Sister Irene's and Frenchie's confrontation with Valak, it tries to kill Frenchie. That's when Irene comes to save him and Valak throws her away. Somewhere between this Valak possessed him.
Here is what Ed says during the end,
Take Maurice Theriault. His friends called him Frenchie. He was a French-Canadian ...
No, he might have somehow tricked the protagonists into believing that he was sealed, as he had already possessed the French man before they attempted to seal him.
Another possibility is that, being a demon and having no physical body, he might have left a little part of himself in the French man, which made him maintain his connection to this world, and ...