While in the Boyle farm kitchen, Jake tells Terry to go get the Grandmother Dough while he assembles the cousins. In the very next scene, the cousins are assembled in the barn, where the Grandmother Dough was kept. Terry did not bring it into the house as requested.
A DNA test of hair from several potential suspects would take days, especially in a rural area, and even more if it were to include lineage and not just comparison of a single hair from a crime scene with that from suspects.
When Jake calls everybody into the barn to look at Pappy Boyle he checks Pappy mouth and finds blisters. There however is no body in the casket when he does this though.
The Grandmother Dough is said to still be good, but sealed in a stuck jar, after more than 100 years. Sourdough starter must be fed frequently, which would be impossible if the jar had been stuck shut. It can last a bit longer if refrigerated, not left out in an exposed barn, but that would, at best, add a matter of months to its lifespan, not centuries.
In the initial release, the scene where Lyndon hugs Pappy showed Pappy's missing left hand as a green screen glove worn by actor Hal Alpert that should have been digitally removed. This mistake was corrected when the effect was later completed for streaming and repeat viewings. The green screen glove is also seen later, when Lyndon is talking to Pappy in Pappy's office. This was not corrected.
When Holt looks out his office window, the rooftop balcony is absent and he can see straight down to the street.
When Raymond looks out his window to see Kevin running towards the precinct in the rain, the view is from a second story window. The detectives' bullpen, and Holt's office, is on the fourth floor.