If you followed the procedure set out in my previous post (sorry, I was not clear that you’d used Bear) it will have exported entries from Day One in folders that reflect your Day One tags (assuming you use them). After import into DT what I then did was to tag the entries within those folders appropriately in DT, batch rename each entry with long name creation date (simply because I preferred that) and then drag and drop the entries wherever I wanted them within the DT database.
If that exercise produces duplicates (because you have entries in Day One with two tags that are therefore present in more than one imported folder) you can select the duplicates, right click and convert them to replicants. In fact in my case because I finally put all entries into a single folder the replicants then vapourised automatically. 
In other words and putting it more briefly, I used the imported folders in DT to assist me in tagging correctly within DT.
I hope this helps and that I’ve not missed completely the point of your post!
Stephen