in my understanding that only new line will appear while the old one will not fade away. you will also see very dim lines which later on life will become thicker.

for example if you see a dim fork on your marriage line then later on this will become deeper and don't think that dim line will dis pears, because they suppose to grow only thicker. keep in mind that new line will form while old one remains.

 
look at this link as a evidence of how much they could change and you will also notice that dim lines later become thicker and you will also notice that the old one are still there.

http://www.palmistry.com/palmistry-news.php