That is one step forward in the right direction with the contrast via MRI. It will either make you nauseous, constipated, or have major bouts of diarrhea. So just be warned.
MRI has progressive levels, just like anything else. When you just want a surface-level evaluation, a basic MRI is all that's needed. Until you can elevate to something deeper as more information comes in, contrast is used, just in case if there are suspicion of cancers, tumors, irregular growth, compression, or lack of visibility to the standard approach. Yes, there are issues with medical professionals and their initial judgments, but they did take a progressive approach through their evaluation. Normally, it doesn't take this long. It's immediate when something cannot be found. The long delay is basically due to medical negligence and insurance coverage issues. They both go hand-in-hand.
Sciatic nerve is merely a precursor, or an indicator, of something else that is happening. It's not the root cause. It's not an untimely causal effect. It's merely a branch of side effects that provides a glimpse of something else that is occurring at the same time, but lying more dormant with very little noticeable differences compared to before the main injury. To give a rounded example:
For the past 20 or 30 years, everything seems like they should be. Nothing is wrong. Once in a while, you get a tingling of the left side more than the right side when you overworked the muscles. Everything works normally like they should. Sometimes, you sit for too long on the toilet seat, minding your own business, and after sitting for too long, you simply get a numbing sensation. Nothing to pay attention to since your mind is blocking everything out, considering the numbness as normal. But behind it all, the left side is more tingling than the right. Forward to 5 to maybe 10 years ago, something may feel "off". Left side of the scrotal sac and the butt cheek tend to be off a bit more, but very little that you don't notice. There may be more sensitivity to the left side of the penile shaft, heightening the pleasure on the left more than the right. Nothing noticeable enough to warrant any extra caution. It's more of a bonus than a caution. You probably fell on your butt, like so many of us, brushed it all off as human errors and stupidity, and not worrying about anything since nothing was out of place. Little by little, a compression of the nerve and the discs are mounting.
But things add up. It's like a blocked fuel injector in the car. Sometimes, the car gets a burst of speed out of the blue, and you're thinking the car got some extra horse because of the fuel's additives. Sometimes the car just sputter out of the blue, where the RPM dips and rises by a few hundred, but that's just too small to detect. That is, until the car's RPM dips into the low or the high RPM way above the normal, causing major sputtering or surging, which then you finally notice something major had happened. It's not the dashboard, the electrical, the transmission, or even the driver. It's a localized fuel injector, clogged fuel line, or even the fuel pump. It's somewhere upstream, in the middle, but it affects everything downstream. WE DON'T KNOW. Just like your car, you run over speed bumps and pot holes, and nothing comes back as major. Little by little, one of your sway bar links, the mounting bolts, boots, and covers started to wear out from continual impact effects. You may not notice the subtle changes until noises, squeals, rattling, and breakage finally manifest. It's not the wheel itself, the wheel bearing, or the suspension (upstream) that affects everything downstream. We know which side, but we don't know what's damaged upstream until we diagnose one part at a time.
These are just some odd examples of downstream damages that have relevance to the case here. What we may not detect as anomalies, we ignore until the anomalies finally manifest into a full-blown issue. Just like where you are now. You may not have detected some small anomalies to register as possible incoming major changes, until an injury, or a downstream compressed nerve (your penile dorsal nerve) triggered something way upstream. It may be sciatic, it may be pudendal, or even peroneal terminal points, but it all point out at the terminal points between the L and S. Just like a mechanic, a professional medical person must systematically evaluate one step at a time and rule out all possible issues. If we have to blame medical personnel for incompetence, we have to pretty much bring in every professional of all types across the board. It's about how experienced each individual is at their job.