Helional
Hi, I'm Neiltonks (talk · contribs). I've accepted your revision on the January 5 article (though that doesn't mean another editor won't still revert it, as which events are notable enough for inclusion in these 'date' articles is a notorious grey area!)
You were wondering why your previous attempt to add this information was reverted by another editor, and I think I know why. I'll explain it to you so that you can avoid similar situations in future. Basically what happened on the 12th of November was:
- 13:26 - you added the Venera 5 update, without a reference at that point.
- 13:39 - user Deb correctly reverted it as unreferenced.
- 13:55 and 14:01 - user Deb added references to some other previously-unreferenced entries further down the article
Following this, at 14:55, you re-added the Venera 5 update, with references. However, when you did this you edited the revision of the article which was created by your original (13:26) edit. At that point this wasn't the most recent revision of the article (that was the one created at 14:01). If you edit an old revision, the result is that the edits which have been done since that point are lost. In this case, you lost the edits made by user Deb at 13:55 and 14:01. I'm sure this wasn't intentional, though. User DannyS712 noticed that your edit had caused the references added by Deb to be lost, and therefore reverted your edit in order to restore these.
Editing an old revision is a simple mistake to make, and we all make mistakes so I'm not blaming you for what happened, simply explaining it.
Unless you specifically want to remove some past edits, you should always edit the most recent revision of an article. If you're editing an old revision, a warning is displayed near the top of the edit screen saying "You are editing an old revision of this page. If you publish it, any changes made since then will be removed. You may wish to edit the current revision instead." but I guess you didn't see this as the top of the edit screen is admittedly rather cluttered with messages in varying colours!
Anyway, I hope this helps explain things. Please don't be discouraged from editing in future: as I said, we all make mistakes.