Nutrient imbalance or healthy development?

Looks like a combination of phosphorus deficiency, end of life with a bid of nitrogen deficiency and cold nights. Starting with phosphorus. Your 3rd picture of week 19 you can see the serrated edges curing up on the leaves. This is the first sign of a lack of phosphorus ( also a first sign of high heat or low humidity but your heat is normal and humidity is high so you can rule that out). The next sign is leaves start to go purple ( this is also genetics and will happen based on pigmentation and not a deficiency with some strains when they hit end of life or low night temperatures.). The spots and purple leaves going brown is the next phase. Nitrogen deficiency- this is seen with the bottom leaves going yellow/red( strain pigmentation I mentioned above ). Nitrogen is mobile so the plant will take the nitrogen from the lower less productive leaves as it needs it. This is normal for end of life and actually a good sign you did not over feed her. To much can cause a harsh smoke and bad taste or take longer to cure the bud after it has dried. As for what you can do I would say keep her happy with water until harvest. With your location you only have so long before it gets to cold. She can handle a short frost but Its best to harvest before that.