Experience of big difference between Elo and national rating? I was just wondering if others have experienced big differences between players Elo and their national rating?

Currently I am playing a tournament outside of my own country. The tournament is Elo rated and expected scores etc are of course then based on Elo. My own Elo is very close my my national rating, around 2050 both of them.

However, in this tournament, a big swiss, I mostly face players around 1600-1700 Elo and they play incredible strong for such a rating.

After the games I ask what their national rating is, and for all of them it's around 2000-2100, which makes more sense. But then the expected scores that are calculated using Elo is hugely in favour of them. It seems the Elo system, is not really accurate in this situation.

Have other people experienced such a huge difference between national and Elo rating?
For one opponent the difference was even around 600!

I guess this situation occurs because very few tournaments in this country are Elo rated leading to the two ratings to be wildly out of sync.

Unfortunately, for me this has the effect of pretty much being mathematical doomed to lose a lot of rating in such a tournament.
As you suspect this can easily happen, if only very few tournaments are Elo rated, and the players are still developing in strength. The problem is often exacerbated by the lower k-factor in Elo, which means that Elo changes more slowly.

Despite not really being an up and coming player anymore, my Elo is still catching up to where it should be according to my national rating and, alas, I expect that to continue for quite some time.