My yorkie is 100% potty trained to go outside.
Up until last year she would occasionally have accidents in the house, but hasn't had one since my golden retriever passed. Now I think she was having accidents because Lucy also having accidents in her old age? It would often happen on the same day.
I think at 4 1/2 months your baby is doing very well!! I know Lexi wasn't at that stage at 4 1/2 months
But by 6 months I would say she was about 90%.