The abbreviation rule of a measure word In the following sentence:


  昨天晚上买了张彩票，结果中奖了。


If I understand it correctly, 张 means 一张 but 一 is omitted here.

Also, if you want to mean it in plural (i.e. buy multiple lottery tickets), the sentence should be the following.


  昨天晚上买了些彩票，结果中奖了。


Now, can I also omit 张 as well, to make the sentence the following:


  昨天晚上买了彩票，结果中奖了。


In this case, does the sentence mean singular, plural, or both (which makes the meaning dependent on context)? Or is the sentence invalid grammartically in the first place?
“昨天晚上买了（一）张彩票，结果中奖了。”，it indicates you buy One ticket. You'd better use 几张 to indicate that you bought several tickets. I am not saying you are wrong by 买了些彩票, but in practice, 些 is often used to describe uncountable nouns. For example, 我买了一些水果。这些事情。说些什么？

you can say '昨天晚上买了彩票', which conveys the fact/behavior itself you bought some/a lottery ticket(s) (how many you bought is not the point/important; Or you deliberately don't want to tell how many you bought; Or people don't care the number of tickets you bought.)