If I remember correctly the last time this was brought up is that there is a limited premium. The reason it is limited is that "earliest known dates" of use (EKU) are always changing. I've found a couple myself based on Scott but then further research showed Scott's info to be out of date and earlier usages had already been found...
I know that Scott's lists the earliest date of issue for most of it's stamps. I remember someone started a thread about this once but I can't remember much about the result. If I were to find a post mark giving an earlier date of issue than the one listed is there a significant amount of money involved and are there collectors for it? Just curious, I don't have one as far as I know. I just am curious whether it is something I should watch for.
re: Earliest date of issue
If I remember correctly the last time this was brought up is that there is a limited premium. The reason it is limited is that "earliest known dates" of use (EKU) are always changing. I've found a couple myself based on Scott but then further research showed Scott's info to be out of date and earlier usages had already been found...