Here's some letters that can be misunderstood or misreported when you're looking for someone you know "should" be there. Many of you will be familiar with these. Anyway, I hope these may help.
Similar sounding letters:
A clerk or enumerator might misunderstand a spoken name. Like my Perrin family can be reported as Berrin or even Baron.
B=P or P=B (all of these can be interchanged, btw).
V=F
T=D
S=Z
J=Y, some Germanic names start out with a J pronounced like Y, then get changed.
Spelling:
The joys of deciphering penmanship!
F=PH
L=S - in old handwriting, as many of you already know, the small 's' looks like an 'l' compared to modern handwriting
M=N
V=W
I=J
N=V