This is one of the things that is preventing the manufacturers from endorsing Biodiesel. It has been a problem from the beginning. NREL tested Biodiesel from most US suppliers. 85% met the ASTM D6751 standard. 18 out of 50 samples were not B20, even though they were supposed to be. 2 samples were B100, one was less than B5. Fuel distributers also don't currently differentiate between ULSD and LSD when blended with Bio. Lastly, only one sample of Biodiesel passed the B100 Rancimat test (test for fuel stability).
... . and the list goes on.
Fuel certification is the next major hurdle for the industry. Expect opponents to make the most of it.
Joe