To keep track on my cost and to locate any glass I did this in my iodentification.
Say my actual cost was $11.25 I did this.
then to locate it in my inventory I did this.
The S7-25 tells me it is located in my tray S7- case  and glass number 25
This will give you a basis to decide your making an offer to trade or purchase.
I hope this will help you in your need to add to your collections.