Most of us don't use them - they are pretty "old school" in that they happened to be sort of close to a squirrel's needs at a time when there was next to nothing available for them in the animal food trade. It would not surprise me - most animal feeds change source ingredients constantly based on what they can find at the best price. The end result has the same ntritional numbers but every lot can have different ingredients from different places.
Have you ever looked into the Henry's food? Pretty much everyone here uses it. It was designed to provide all of the nutrition they need AND taste good. They are only available online:
https://www.henryspets.com/squirrel-diet/ - and of the first three items on the page. he picky blocks and the hazelnut blocks are favorites around here. All human grade ingredients and no preservatives - keep them in the freezer. 2-3 per day provide all the nutritional needs for an average squirrel.
Most of us also "free feed" Teklad blocks. They are a very high quality "lab diet" for rodents. They are marketed to the laboratory customers in 50 pound bags but a lot of people repackage and sell on ebay. That is where I get mine:
https://www.ebay.com/itm/23385020909...AAOSwyjBW5xS~/ The 14% protein variety is what you want. 5 pounds of these last a LONG time. My boy gets 2-3 of the Henrys and I just make sure he has a couple of the Teklad available if he wants them.