My experience with grendadine fina:
Having ordered bespoke from 2 makers (Cappelli and Hober - and both are great), my recommendation to others is to order 1 inch shorter than you usually order. Both seem to stretch / wear longer, really even at the first tying of the tie, it is not like it happens over time. Not sure on the dynamics of why, doesn't really matter to me. Not a big deal, just one of those little learnings to pass on to others.
A good point about stretching - unfortunately stretching is more of an art than a science as there are a number of variables.
1) Grenadines are a loose weave and do have a tendency to stretch - some stretching can happen the first time that you wear it and more stretching can happen over time.
2) The more you wear a tie the more likely there will be stretching.
3) Tying a tight knot tends to increase stretching.
4) The longer a tie is the more that it will tend to stretch. As an example a 64 inch tie will stretch more than a 57 inch tie all things being equal other than the length.
5) Some men do not change their grenadine tie length and are very happy with little or no stretching. While others need to shorten their grenadines by an inch and others by two or even three inches.