It use to be valid only "sePtimebre" until a few years ago. I can find the date, may be 2000+something. Now "setiembre" is also valid. It looks like it's popular in Peru, but sometimes it's used here too. (When I say it, the "P" is weak, probably closer to "seBtiembre", but it's there.)
The tradition is Spanish is to keep the orthography synchronized with the oral form, so if some variant gets too popular it's included in the RAE dictionary and later if the old form is unused it's deprecated.
It's very different from English, where the oral and written form of a word may be almost disjoint.
> The tradition is Spanish is to keep the orthography synchronized with the oral form
Interesting, I guess that makes sense. I love how phonetic Spanish is, but I hadn’t considered that it means the spelling needs to equally evolve with the language in order to stay that way.
The tradition is Spanish is to keep the orthography synchronized with the oral form, so if some variant gets too popular it's included in the RAE dictionary and later if the old form is unused it's deprecated.
It's very different from English, where the oral and written form of a word may be almost disjoint.