Apple made an official statement about a year ago that they do not want podcasts to have the episode number in the episode title field.
Some of the podcast listening apps, including Apple, number the episodes within the app natively which has nothing to do with what's in the title field. They do this so they can have control over numbering and uniformity throughout their applications.
In the past podcasters have published what they would call 'episode zero' or an inaugural episode, which is the initial episode, and not call it episode one. However, the listening apps see it as episode one, whether you call it that or not. So then episode zero would be episode one, episode one would be episode two, and so on. There is then this inconsistency in the automatic numbers natively beside each episode and the one manually placed actually in the title field.
Additionally, Apple Podcasts has now created the ability to have a trailer episode, which essentially would take the place of an 'episode zero'. It will be pinned to the top of the lineup within the app. Trailers are exempt from the automatic numbering in the app (lineup). However, that's only on Apple Podcasts. That doesn't necessarily apply to other apps, like Spotify, iHeart, or Goodpods. This causes further confusion and redundancy, so we don’t recommend numbering your episode titles.
Lastly, when the episode number is placed in the title, especially at the beginning, that takes up some very valuable space for characters at the beginning of the title. Most apps only show so much of the episode title in it because it’s truncated. Meaning, it cuts it off after a set number of characters for the user to expand upon engagement. Less of the actual title would be visible hindering users' ability to quickly judge if that episode would be worthwhile.