Someone correct me if I'm wrong, but 算 can also mean "to regard as"? For example:: 那我们算认识了 Then we'll regard this as having gotten to know each other (Clumsy sentence but this is the way I'd think about it to understand 算 a lot more clearly) So in the translations that were given, I'd understand 就不算 in this way: If you haven't seen a Sid school's Christmas production, then you can't regard yourself as having seen one at all

Bacically it means "that doesn't count" or "you can't say that you've done something." So, if I translate the sentence "如果您没有欣赏过特殊儿童学校为您呈现的圣诞汇演，那么您就不算看过真正的圣诞汇演" back to English, it should be "Before you see the performance given by SLD school, all the Christmas performances you've seen can't even be counted as real Christmas performances." Or, "You can't say that you've seen a real Christmas performance until you see the one given by SLD school." 如果您没有到过北京，那么您就不算到过中国。 "If you even haven't been to Beijing, then you can't say that you've been to China." 如果你不知道“侬好”是什么意思，那么你就不算是一个上海人。"If you don't even know what "nong hao" means, you can't be counted as a Shanghainese." Hope that I may be of some help here :)

Actually,算 is very oral,and we often use it in a negative sentence （不算是...不应该算是...不能算是...）even if we use it in an affirmative sentence, it has also a sens of "not completely,not exately" or when the speaker is not very sure.（算是：这算是对她的补偿吧！） you may take it for "regard",but we often use "把...当作..."or "把...看成" to explain "regard...as...". sometimes,these two expressions can not exchange their places in a sentence.

Yes, Rudi got it right. 就不算means "you cannot say" "you cannot regard " Basicly, 算 means "calculate, count" in Chinese. We can understand 就不算 as " cannot count ....into ..." you can also say 就不能说 as an instead If you haven't seen a SID school's Christmas production, you can't count yourself into those who have seen one at all.