A completely blocked vessel can open collateral vessels that will provide a natural bypass. That's not say that partially blocked vessels do not develop collaterals!
I have a completely blocked LAD just below the branch off the main artery that was discovered 5 years ago. It is obvious by the history you provide there are collateral vessels that supply the blood to areas deficit.
The AAC/AHA guidelines do not recommend stenting any vessel occlusion less than 70%...there are exceptions such as associated chest pain that cannot be relieved with medication. Stents can be problematic, and I don't believe the 60, 40% blockage should have been stented...but? there was cardiac arrest.
Fives ago, I didn't have cardiac arrest, but I was admitted to ICU for congested heart failure. At that time a stent implant for the 98% RCA, circumflex 72% not stented, and the 100% LAD occlusion remains. Medication controls any chest pain when I workout 3 times a week. I feel quite well, and have no problems except with unusual exertion.