[1] [2] Blood levels of B12 may rise quickly following injection, though elevated blood levels do not immediately translate to symptom resolution
doi: 10.1016/S0022-3999(01)00315-4 Summary Keywords Sensewear armband, myalgic encephalomyelitis/chronic fatigue syndrome, vitamin B12 nasal drops, vitamin B12 serum concentration, RAND 36 questionnaire Citation van Campen CLMC, Riepma K and Visser FC (2019) Open Trial of Vitamin B12 Nasal Drops in Adults With Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Comparison of Responders and Non-Responders
and T.M
"Gastric pentadecapeptide BPC 157 reduces monoarthritis-induced pain, enhances wound healing, and improves tendon integrity in rats." Journal of Pharmacological Sciences , 104(1), 5968
For comparison, see what happens when semaglutide is left out overnight
The anecdata seem to indicate that the mode of delivery, that is whether or not systemic or local, doesn't seem to matter that much