If it is from one forumite, then report just one post and state in the report that there are other similar post in other threads, and as I've said it is easier to just look at their profile and check their post history and we can delete posts from there without going into threads and delete it one by one...
My take from here is, and this is what I am doing now:
When I am seeing someone is spamming with same contents then I am archiving their post history. From all these same contents, I am reporting 2/3 posts with the comment like "spamming with same contents. Please review post history ".
I've archived peoples posts before, but only for long term. When I recognize a name I refer to my list, and see if they are on it. If they are then I report one of their comments with the archive of the previous posts. However, this is over a long period if you are reporting them within short period like a hour or so then you likely only need to report one of their posts, and ask the moderator to check their post history.
I'm not saying it's bad practice what you are doing, but is likely a little unnecessary if you are reporting them in the same period.