Pretty much same answer as above. The default onUnknown of pircbotx only grabs whatever the “line” sent to the server is, which in the event of the new resub notifications is really short and doesn’t really give much info. In order to properly grab them, you’ll have to download the source code of pircbotx and alter the onEvent/onUnknown event functions to send whatever it is that you would prefer.
For example, I personally altered mine to not only have tags sent through, but to also send the full raw line through in the event of any future changes, that way I can handle them on my own.