Not a screener, but my 2 cents about the topic since I uploaded a number of old scans here.
Basically the general upload guidelines apply, but there is a small exception for old scans under 1.1.2 Uploading scans

"For such shots lower standards are applied. If it is necessary to clone out damage to the photo, please leave a remark in the comments to the screeners field. Guidelines for composition or obstruction do not apply to rare old scans."
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Scans must be of course in a an acceptable quality but may require some editing in PS or LR. They go through the normal upload approval process. Always leave a comment for the screener that it is a scanned slide or photo. I take it that any uploaded scans come from slides / photos taken by yourself; shots from your collections may require different attention (in the past there was a rule to create a separate account for that, named "A310Productions Collection").

Happy New Year,...