Bash: rename duplicates for generated values in csv file - bash

Question

There is a bash script that create a email addresses in next format: first letter from name and full surname, lowercase +#example.com.
csv file:
id,location,name,email
1,1,John Smith,ab#dc.com
2,2,Paul Robinson,
3,3,Fidel Guererro,qw#er.com
4,4,John Smith,
...
Column Name can contain duplicates. In this case script should add 1 in email address (ex. for id=1 - jsmith#example.com, for id=4 - jsmith1#example.com).
I try next script:
#!/bin/bash
while IFS=, read -r col1 col2 col3 col4
do
if [ "$col1" == Id ]; then
echo "${col1},${col2},${col3},${col4}"
continue
fi
firstinitial=${col3:0:1}
surname=$(echo $col3 | cut -d' ' -f2)
if [[ $col4 == $col4 ]]; then
col4=${firstinitial,}${surname,,}1#example.com
else
col4=${firstinitial,}${surname,,}#example.com
fi
echo "${col1},${col2},${col3},${col4}"
done < acc.csv
I recieve all addresses with 1.
How can I change this script?
Expected output:
id,location,name,email
1,1,John Smith,jsmith#example.com
2,2,Paul Robinson,probinson#example.com
3,3,Fidel Guererro,fguererro#example.com
4,4,John Smith,jsmith1#example.com
...