I’m glad you’re enjoying the tagging. It would be nice to label the past participle that way but that isn’t how we get the information I’m afraid. We are still working to improve this but I would think Participio is most likely to be the label since it does appear in so many different tenses.
Yes, the endings are a tricky one. There isn’t much we can do there I’m afraid. For the most part, the past participle appears in the o form. For the other forms you will just have to know that and tag them yourself if you like. In fact, if you just learn the base form, the other forms are easy enough to figure out.