awk adds extra comma at several places

Question

i want to add a timestamp with awk to a CSV-file. To generate the timestamp works, but the result CSV-file have some extra comma at several places. How can I fix the problem?

origin-CSV (1st line):

time,latitude,longitude,depth,mag,magType,nst,gap,dmin,rms,net,id,updated,place,type 2015-03-13T07:53:53.950Z,38.838501,-122.8300018,3.01,0.18,md,9,93,0.004285,0.02,nc,nc72410280,2015-03-13T08:08:04.639Z,"9km W of Cobb, California",earthquake

awk:

awk -F"," 'BEGIN { OFS = "," ; print "time","latitude","longitude","depth","mag","magType","nst","gap","dmin","rms","net","id","updated","place","type","timestamp"} NR>$0{"date +%s -d"$1""| getline dte;$17=dte; print}' origin.csv > result.csv

I was surprised that it worked only with $17 instead of $16, although the timestamp-column is the 16th.

result for the 5th line:

time,latitude,longitude,depth,mag,magType,nst,gap,dmin,rms,net,id,updated,place,type,timestamp 2015-03-13T06:46:45.450Z,-55.1707,-128.8193,10,4.9,mb,,116,31.469,0.59,us,us10001m1z,2015-03-13T07:36:31.510Z,"Pacific-Antarctic Ridge",earthquake,,1426229205

here are two commas instead of one.

Answer 1

@Archemar
oh man, so stupid. That solved the problem. Deleted row "type" and "place" (fortunately I don't need them) and now it works ... thanks so much for taking a look