1. at 还是 on

单就 date 来说，它既可搭配 at 也可搭配 on，两者的区别是：若 date 表示 day 的意思，则搭配 on（指具体的某个日期）；若 date 表示 time 的意思，则搭配 at（笼统地指某个时间）。比较：

Theatre tickets must be used on the stated date. 戏院门票必须在规定日期使用。

The details can be added at a later date. 细节可过些时候再补充进去。

2. 用 at 的更多例句：

It's an idea that may be worth revisiting at a later date. 这个观点值得以后进一步探讨。

The lines were interpolated into the manuscript at a later date. 这几行文字是后来加到稿子中的。

Never put anything down on paper which might be used in evidence against you at a later date. 不要在纸上写下任何东西，免得日后成为对你不利的证据。

Your suggestion will be brought before the committee at a suitable date. 你的建议在适当的时候要提交委员会。

We agreed to consider the matter again at a future date. 我们同意将来某个时候再来考虑此事。

The meeting will take place at an unspecified date in the future. 会议将于日后召开，具体日期不确定。

A handsome young man is in love with a beautiful girl, we all wish they be married at an early date. 一个英俊的青年爱恋一个美丽的姑娘，我们都祝愿他们早日喜结良缘。

3. 用 on 的更多例句：

Come on the same date next year. 明年同一天来吧。

We hope to deliver the goods on the agreed date. 我们希望在约定的日期交货。

The aid did not arrive on the promised date, giving us the unpleasant feeling of having been run out on. 援助未能按约定日期来到，这使我们产生了好象被人抛弃了的不愉快感觉。

Legal counsel will negotiate with the official on the implementation date for the new regulation. 法律顾问将与官员协商有关新法规的实施日期。

我的理解是这样的：如果是具体的日期，要用on. 如千千老师的例句， on后面都用了定冠词the。但网友的问题不涉及特指，因为用了a later date。因此，就at/on a later date 而言，二者都可以。用at更多见。用on多见于美国英语。似乎美国人对on情有独钟，如on weekends, on the street, on the exam. 在英国英语里，一般说at weekends, in the street, in the exam.

请看几个外刊例句：

个人理解，仅供参考。

我在BNC语料库查了一下，on a later date的总次数为1，at a later date的总次数为292。

顺着奉老师的方法，我在COCA语料库也查了一下，on a later date的总次数为11，at a later date的总次数为750。供网友参考：