This is important for the accountability to all your colleagues. Note that, unfortunately, this is why you do not have typed feedback for this author. This helps the author know that they missed out on important feedback. But, tell them that you have some less extensive comments to help the audience in their critique as well as a few synthetic comments to tie the papers together. If the paper is severely late, you can explain that you just did not have time to review due to its lateness.
Papers are of varying quality.
It is important to acknowledge that the papers are at different stages of progression. If you note this in a developmental way, it is encouraging to authors, but also helps the audience realize that all are not of equal quality. When critiquing the papers, emphasize how the paper can be improved, not how it is weak. The papers are not strongly related to your research expertise. If you have a colleague who can read the paper and clarify issues for you, this can be very helpful.