After a slight hiatus (at least 25 years) I dug out my tools & the 1/2 side of 2.5mm Tandy leather I still had. A tad green in places & a little..ahem...firm, but it was still useable after a little TLC. 
I have only used it for projects that are "backed" - clocks, keyracks etc. & although a little problematic to cut it worked ok. 
So absolutely no need to throw away any leather any time soon  
Example of the old leather!