For over 9 years I have used the last 4 numbers of the item number to keep track of the earrings that I sell. This system has always worked well for me.
Occasionally, more like rarely because I am very careful, I start with the 5th last number and omit the last one.
For example, if the number was 123456789123 the number I use would be 9123, or 8912 if I made an error.
When I went to pull the products after ending them tonight, the majority of them had an extra number on the end, as though I had made the above error multiple times.
These were all GTC listings. The chance that I made that many errors is slim to none. Is eBay changing the Item # when they relist automatically? I can't think of any other reason for this happening.