If you know there's a possibility (as there is in this exchange) that you might only get <500 words, it makes sense to give some prompts that can be quickly dealt with, if you are bothered about getting what you want in a shorter fic. If you don't care what you get in a shorter fic then sure, let the author go ODOA if they want to write something shorter.
I'd rather have 500 words of something I've prompted for than 500 words of something ODOA.
Re: Chocolate Box - Letter 3T1L
If you know there's a possibility (as there is in this exchange) that you might only get <500 words, it makes sense to give some prompts that can be quickly dealt with, if you are bothered about getting what you want in a shorter fic. If you don't care what you get in a shorter fic then sure, let the author go ODOA if they want to write something shorter.
I'd rather have 500 words of something I've prompted for than 500 words of something ODOA.