It could be a mistake, but I’d like to think this is a case where the subject of the verb has been omitted because is is optional when it is a personal pronoun like “fe”, like it is in literary Welsh. Assuming that this is the case, then all four examples are good!
If you don’t like this theory, then Hector’s is probably even better
As Louis says - they’re interchangeable. You would always use the fe if you are emphasising, but otherwise it depends on the feel of the sentence, the mood of the speaker, and possibly even the weather or the 6 nations rugby result…
The person (fe hi etc) often gets left out when you’re not talking about a specific thing, so if you think of the starty of an excuse - Well, it’'s like this see…" Wel, mae fel hyn ti’n gweld…", whereas if you’re talking about something specific, you’re more likely to use the person. But that is not a hard and fast rule, and is just something to note in passing and then forget…!