A Comment For Modern US

What a wealth of info this topic has provided. As a newbie I only discovered the varieties that can be collected when getting the 2022 Waving Flag Forever definitive. One tip, it is easiest to get all varieties within the first year as the USPS provides that window to order small portions of stamps from the coils of 100 and greater amounts (well unless you run a business that actively uses mail, but even then I don't see the need in some cases as business with such volume may qualify for a discount rate depending on the nature of the business and how and what is mailed).

The Waving Flag coils turned me on to collecting those stamps with pane and coil format varieties. Haven't gotten to pursuing errors though.

Have you tried Mystic Stamps?

They are a good source for most things US Stamp related.

I'm looking at their page on the 2001 - 2002 stamps you have pictured. They have many of the varieties listed. While their prices are CV or above, at least you know that you will be getting the correct variety you need.

Also their catalog is free (or least it was last time I checked) and can serve as a checklist with pictures for you. It is also a great substitute for Scott's; cheaper and they are just as up to date. Their website is the most up to date catalog I know of.

Does anyone know if there are similar guides for the Christmas stamps?
I have lots of these piling up for several issue years because I don't know where or what to put into my H.E. Harris album.
Yeah, I know I said Mystic's catalog was a good source. But I was wrong. I apologize for that post.

https://stampsmarter.org/features/Id_US_RegA.html

Click on the 'View By Series' tab and then select 'Contemporary Christmas' to view all US Christmas stamps (through 2019).
Don