It really varies by school. But a lot of schools know that you can't really convert scores from many international schools... It just doesn't work out well. So, they tend to look at your performance relative to your class. This also helps to take into account that some schools are more competitive/challenging than others. But overall, it will really depend on each school that you're applying to.
That's good that your grades improved over time. Naturally, high grades all the time is ideal, but schools are very willing to believe that you grew more mature over time, as long as you provide good evidence of that.
And the chess thing is good! Don't be afraid to talk about that in your app. Don't present is as an "excuse" to cover for your lower grades, but instead use it as a means of showing how you have passion for something (and why).
For undergrad transcripts, b-schools usually want to see official transcripts that come straight from our university (signed and sealed; you don't even get to see them). My experience may be different than yours since I went to college in the U.S., but my undergrad college was great about handling them efficiently. You can call the registrar's office at your old school and they'll know exactly what to do. Just be sure to give them plenty of time. DON'T leave it until the last minute!
Best,
Scott
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Co-Author, Your MBA Game Plan