It was a mistake on your part, but a very understandable mistake.
You submitted a request to add the 1970 documentation, then a separate request to add the 1971 documentation.
The 1970 one was approved, modifying the original comments to include it.
Next, the 1971 one was approved. But because the 1970 documentation was not included in your 1971 request, it was deleted from the newly-approved comments.
To avoid that, you would have had to submitted a request to add both documentations within the same request.
I hope that makes sense.