The spellings of place names probably tend to have changed more in the Celtic regions of the country as they were originally in the local Celtic language. When this ceases to be in everyday use, being replaced by English, the meaning of the names gets forgotten and they change/become corrupted over time. Trenowth is a good example of such a name in Cornwall, it would have originally been Trenoweth. Tre means a settlement such as a farmstead or village so Trenoweth is "New Village".
Oll an gwella (All the best)
John