Image imported from derpibooru 
Original Description:
 
(Fixed version of >>2672013 with two missing designs and three design variants added)
 
The 134 MLP shirt designs on Merch by Amazon released between February 2020 and August 2021, sorted by the production codes shown in the listings. Numbers that were skipped are shown as blank rectangles. Image created using ffmpeg, Inkscape and ImageMagick.
 
The links below are to the Amazon US listings for the T-shirts with the designs.
 
19HBLP  
01, 02, 03, 04, 05, 06, 07, 08, 09, 10, 11, 12, 13, 14, 15, 16A, 16B, 17, 18, 19, 20, 21, 22, 23, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 38
 
20HBLF  
01, 02, 03, 04, 05, 06, 07, 08, 09, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 23, 24, 25, 26, 27, 28, 29, 31, 32, 33, 34
 
20HBLP  
01, 02, 03, 04, 05, 06, 07
 
21HBLF  
02, 04, 05, 06, 09, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21A, 21B, 21C, 22, 24, 25, 27, 28, 29, 30, 31
 
21HBLP  
01, 02, 03, 04, 06, 07, 08, 09, 10, 11
 
21HBLM  
01, 02, 03, 04, 05, 06, 07, 08, 09, 10, 11, 12, 14, 16, 18, 19, 21, 22, 23, 24, 26, 27
 
Tracking spreadsheets: Merch by Amazon, G5 merch