Split file based on pattern - awk

Input file:

$ cat address.txt
Mr X
Koramangala Post
3rd Cross, 17th Main
PIN: 12345
Mr Y
NGV
PIN: 45678
Mr Z
5th Ave, #23
NHM Post
LKV
PIN: 32456

Required: Divide the above file in sub files each containing one address (One address being from the name of the person to the PIN number)

$ awk '
BEGIN{ fn = "add1.txt"; n = 1}
{
print > fn
if (substr($0,1,3) == "PIN") {
close (fn)
n++
fn = "add" n ".txt"
}
}
' address.txt

So output sub files files:

$ cat add1.txt
Mr X
Koramangala Post
3rd Cross, 17th Main
PIN: 12345

$ cat add2.txt
Mr Y
NGV
PIN: 45678

$ cat add3.txt
Mr Z
5th Ave, #23
NHM Post
LKV
PIN: 32456

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