The words "some" and "since" don't actually introduce a sufficient condition. Rather, "some" is a quantified term that tells us that some of the group under discussion have some characteristic. This relationship goes both ways.
E.g. Some computers are made by Apple.
This means that, of course, some computers are made by Apple, and importantly, that some things made by Apple are computers. This is because the relationship goes both ways.
The word "since" introduces causal reasoning. Since can be substituted by because or any other equivalent word. These bring up causes.
E.g. Since I ate too much food, I am now full.
This just shows that eating too much food caused me to be full.
I hope this helps. Please let me know if you have any other questions.
