Great post DJR, helpful info.
I'd agree that most dogs seem to have an innate sense to back off when it comes to a snake, which is why they are such wonderful animals, (the dogs), because if you are alert to their behaviour they are likely to have smelled the snake long before you see it. Terriers and Jrussels unfortunately have another innate sense and they are most often bitten.
I found it helpful to have a chat to your vet about how to handle a bitten dog, they will tell you if they have anti venom in stock and who else does in the area (they share) or else they will tell you where to go after hours to save time.
In summary - puffy bite - unlikely antivenom - treat symptoms (swelling and pain). Cobra - depends on size of dog - small dogs, limited time left. Bigger dogs - keep them breathing is most essential - get to an open equipped vet as soon as possible.
(this seems to suggest anti venom shortage has been resolved: https://www.dailymaverick.co.za/article/2023-11-17-sa-well-stocked-with-antivenom-say-experts-as-snakebite-season-looms/)