We haven't looked at the subject yet in the 65 Dearborn running changes thread. Though it's on the list. Exact date will likely never be know since we don't know when each car was completed and the supply would likely have run out at different days based on supply and what color and body style carpet your asking about. At San Jose the vinyl sided no toe pad carpet was used well into 65 production and through the end of 1964. Many months past Sept
http://www.concoursmustang.com/forum/index.php?topic=23013.0For your particular need and to provide you with some help I offer the following information after looking at the data I have over the last couple of hours
Based on the examples I have pictures I have carpet sets without the toe pad were installed in cars built at Dearborn, into Jan 1965. So should help with a Feb 65 Dearborn convertible. Of course real build dates are unknown but your about three weeks after what I found for comparison.
Since you have a convertible the use of trimmed carpet with vinyl side panels is not something you are interested in. For others reading this post none convertible was made in three versions
1- No toe pad with vinyl sides
2- Toe pad with vinyl sides
3- Toe pad with full carpeted sides - no vinyl rocker panel sides