Does Finasteride help strengthen / prevent all regions of head hair from falling out?

You need to continue use of Finasteride to maintain results.  I suggest seeing a hair loss expert now to evaluate and go over your condition and provide you information about your best treatment options. There are great non-invasive options like prp/progesterone and/or hair transplantation. See an expert. Best, Dr. Emer

Minoxidil takes a few months to kick in and then show visible improvement.  In our experience, the improvement eventually plateaus.  Minoxidil and finasteride are the only 2 FDA approved medications available to help with hair loss.  There is a small additive effect (not doubling), of using the two together.  

Finasteride in combination with Minoxidil has been shown to add quality, thickness, strengthen existing hairs and even show regrowth in some people.

Medications like minoxidil and finasteride affect hairs that have altered hair cycles. This is typically the areas that are thinning. Minoxidil and finasteride don't typically affect the areas that are not thinning. These medications don't usually lose potency per se, but the patient may express more potent genes that cause the androgenetic alopecia to progress faster. 

Finasteride can be effective for all regions of the scalp, greatly slowing down hair loss and in many cases resulting in follicles growing new hairs. This includes the strengthening of hairs which are going through the process of miniaturization. The exact same thing can be said for Minoxidil. Both treatments tend to be more effective in the midscalp and crown areas, which probably accounts for why the studies focused on those specific areas. 
Unfortunately, patient feedback leads me to believe that Finasteride and Minoxidil can become less effective over time, so that could be why your hair has started to thin after 12 years of treatment. Your hair does look very thick, especially for a man who has been losing hair from an early age. Consider yourself very fortunate!

The studies which I am familiar with indicated that finasteride showed visible strengthening in the crown and front about 60% and 50% respectively. And this is about what I have seen clinically. I have also seen finasteride strengthen temporal points as well as the donor area but have never seen any studies to confirm this. 

Great question. Yes, Finasteride and Minoxidil may help about hair loss. Both treatments have different mechanism of action and their combination could be the best option. Minoxidil can help you in any area of your scalp. Also, I have some patients with some Finasteride side effects and I recommend them to reduce the dosage to .25 mg daily or 1 mg twice a week. But I will suggest you to make an appt for further evaluation about your hair loss and Minoxidil at any local hair loss specialist. You may need additional treatments for hair loss. Good luck. 

finasteride works on the hairs that you may be starting to lose. When there is miniaturization, finasteride might reverse this