Here we see the wrong line number is reported:
$ nl -b a f
1
2 PENG AM
$ crontab f
"f":1: bad minute
errors in crontab file, can't install.
However here it is correct:
$ nl -b a nn
1 1 1 1 1 1 :
2
3
4 BLA
$ crontab nn
"nn":4: bad minute
errors in crontab file, can't install.