Does twitter button shows tweets or tweets+retweets?

• Will the number on 开发者_开发问答tweet button on my site increase if someone on twitter, without even opening the link, shares the url?
• Can one user make tweet button count go from 0 to 2 in any way?

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• The count should +1 for every tweet or retweet that contains the link.
• If a single user tweets the same link twice the count should +2.

Keep in mind though that Twitter has such a high volume of tweets that tweet button counts will likely be off by a %. Sometimes the count is cached as well resulting in delays between tweets containing the link and the count increasing.