Quick edit - I should have used the term decriminalized instead of legalized.
Basically, if someone were to buy pot that is taxed by the Dutch government then travel to, say, Belgium where pot is illegal & they're incarcerated & sent to trial all on the Belgian tax payer's dime, wouldn't the law makers in Belgium want to have a word with the law makers in Holland?
No historian and I hope my answer doesn't violate the subreddit rules.
First of all, technically the Netherlands never legalized Marijuana. They only tolerate coffeeshops selling it and people consuming it. It's actually a quite absurd situation, because growing is not tolerated, and de jure coffeeshop owners break the law when they purchase large quantities. A couple of years ago, growing operations were even partly outsourced to Germany (where it's also illegal, but police weren't really expecting large-scale growing operations in abandoned warehouses).
Now to your question, I can only answer for Germany: They didn't change any laws. What happened in the last years/decades, however, was that the federal states set recommended limits under which prosecutors should drop the charges. These limits vary from state to state. In North Rhine-Westphalia, Berlin, and Rhineland-Palatinate charges are usually dropped if you carry less than 10 g, while in all other states the limit is 6 g.
However, as I said before, these are only recommendations. Prosecutors might still decide to press charges, or to drop charges under certain conditions, such as community service or mandatory counseling. Bavarian authorities are notorious for pressing charges for absolutely tiny amounts.
Then there's another aspect to this: While no penal charges might be pressed, people who own a driver's license (and that is basically everyone over 18) will most likely lose it, because you're considered "unable to responsibly take part in traffic". To get your license back you need to pass a "medical and psychological examination" (Medizinisch-psychologische Untersuchung, MPU, aka Idiotentest).
Wit the advance of rapid tests for THC and its metbolites in sweat and urine, people don't even have to carry marijuana while driving or be under acute influence, but having consumed several days ago can be sufficient for losing the license. There is currently a discussion going on to establish set limits for THC in the blood, because currently this limit is more or less equal to the analytical detection limit.
As a final remark, medicinal marijuana is legal since 2011, but only for very few conditions, mainly multiple sclerosis (MS).