Please explain my meat dry curing observations

There are several variables that need to be considered to properly and safely dry cure meat...temperature, humidity, ph level, for example. Just on the topic of moisture loss, however...you will not be able to tell simply by looking. People who do this for a living can tell by touching...most of us weigh our product before hanging. In general, when there is a 30% reduction in weight, the meat is properly cured (given that all of the other variables have been properly dealt with).

Meat getting harder means it is drying, however it could be drying too fast. In this case the outside will dry before the inside has a chance to. If this is the case, the meat will not be pleasant to eat, but more importantly you could have a potential safety issue. Proper humidity and temperature will help control this....around 60 degrees F (15 C) and 60 - 70 percent humidity.

As far as salt goes, be sure to use some sort of curing salt.

I recommend reading up on the process. Many things can go wrong and you can make you and your guests sick very easily.

I don't know much about dry-curing in general, but dry-aging of beef, which is a similar process, has been studied in detail by Kenji at Serious Eats. Based on his findings, I would suggest you're running into a similar issue:

So why does meat being aged stop losing moisture after the first few weeks?

It's a matter of permeability. As meat loses moisture, its muscle fibers get more and more closely packed, making it more and more difficult for moisture under the surface to continue escaping. After the first few weeks, the outer layer of meat is so tight and tough that it is virtually impermeable to moisture loss.

According to this source, most moisture is lost during the first few days. They also have this to say:

The final product will weigh 15-20% less than the weight of the original meat. In case of byproducts like liver, heart, kidneys and heart the weight loss can be as large as 34-40%.

So what I'd do is, at the point where you think it's stopped losing water, weigh the meat and compare that to the pre-curing weight. Are you losing the right amount of liquid? Then I wouldn't worry too much about it. Note that Kenji found significant benefits to further aging beef after the water loss had ceased, so that doesn't necessarily mean there's no benefit to further curing.

I think it depends very much on what meat you are attempting to cure. the curing process is not simply about losing moisture but rather developing flavour and other desired qualities such as consistency. many hams, such as Iberico, etc may be cured for an average of 2 years and others as long as 4 or 5 years.

edit: i don't know much about other meats, but i can say that with european hams in general, salting is the first stage and then importantly, is mostly washed off before resting and then eventually into longer storage periods according to the region and method. Its interesting to note that most hams lose the last of the unwanted moisture beyond the six month period, where some of the final changes to consistency and flavour also occur. but I don't know if this is as easily controlled with other meats. the 'longer cure' meats are then moved to a generally dryer environment where they are assessed regularly. trivia: some of the larger ham bodegas have about 5 million euros worth of hanging meat and the most expensive ham was sold in London for about £5000 euros.