I readily agree that there's potential for confusion on the interpretation of the definitions, and it seems some numbers simply don't add up when multiple sources are considered. I'm keenly interested to see what I can do to get clarification on the data, and preferably access to raw data (presumably anonymized/scrubbed). Likewise, I don't have a firm explanation for the drop in vaccinations rates in 2013. The WHO 2013 data is listed as provisional of course, but given the tendency toward the fastest reporting coming from the most heavily populated/metropolitan areas in any given nation, I'm not anticipating a serious shift in the percentiles by the next update period.
I've lived in multiple U.S. cities with large Hispanic populations and also recall a positive attitude toward immunization in those communities. As you noted, upper-middle to upper class white families are indeed disproportionately likely to avoid vaccines in some areas. I happen to strongly disagree with their views, especially given the fact that I have a family of my own whose health matters immensely to me. The harm caused to communities caused by avoiding vaccinations is undeniable.
With specific regard to the drop in Mexican stats, I can't help but wonder if anti-vaccine fear-mongering has gained a stronger foothold in the country, although I certainly can't speak directly to that. There may be other factors as well; perhaps policies of the Enrique Peña Nieto administration (assumed office in 2012) are pertinent, or maybe large-scale destabilization associated with cartel activity has made a difference. This is simple speculation; I honestly have no idea why it's happening. I do note that in 2012, approximately 6.05 million Mexican unauthorized immigrants were residing in the United States, and the previously seen recession trend of declining Mexican illegal immigration appears to have reversed after 2010.