I love collecting stamp varieties, and with my work for one of the main online stamp catalogues I've come to learn that catalogues from other publishers can offer different persepctives on what constitutes variants of stamps compared to the "catalogues of record" for a specific country.
Michel of course is "catalogue of record" for Central Europe, but it also produces a USA Specialized catalogue, the latest edition being released in 2021. I decided to get one to see how Michel views specialized listings for USA compared to Scott.
Here is a sample, the start of the listings of the regular issues of 1870 to 1882. Note that Michel does not separate listings sequentially by printer, but rather keeps them all within the same grouping. Below is the introduction to their specialized listings for these issues and the listings for the 1c values. The big difference I notice here is in paper varieties - Michel lists several paper variants on the Continental bank note printings that Scott seems to completely ignore.
Anyways definitely glad I purchased this catalogue, definitely provides some new potential collecting perspectives for variants compared to Scott.

